Donald Trump’s election campaign is being investigated for possible links or collusion with Russia.

The stakes are high: several former top officials have already been arrested and charged. Some have admitted serious criminal offences.

You can read and watch all of Channel 4 News’ coverage of the investigation here – and get up to speed with the scandal that threatens the presidency.

Latest reports:

The background

Donald Trump was elected 45th President of the United States in November 2016, after winning more electoral college votes than the favourite, Hillary Clinton.

Four months before the vote, the FBI had launched an investigation into possible links between the Trump campaign and Russian officials.

But the new president sacked the FBI’s director James Comey in May 2017, before the investigation was complete.

Then, around a week later, the US Department of Justice appointed Robert Mueller as Special Counsel and tasked him with investigating “any links and/or co-ordination between the Russian government and individuals associated with the campaign of President Donald Trump”.

Mr Trump has repeatedly denied collusion with Russia, calling the FBI investigation a “Rigged Witch Hunt” and an “illegal Scam”.

But veterans of Watergate – which brought down Richard Nixon – say that if collusion with Russia is proved, it would be an even bigger scandal.

Who’s who?

General Michael Flynn

The former US Army Lieutenant General resigned as Trump’s National Security Advisor after just 24 days because he lied about his contact with Russia’s ambassador to the US, Sergei Kislyak.

According to court documents, Kislyak contacted Flynn on December 28, 2016. Barack Obama was still president and had just ordered sanctions against Russia for interfering with the election.

Flynn was in communication between the Russian embassy and members of the Trump transition team. After consulting with Trump’s team, he asked the Russians not to escalate tensions ahead of the presidential handover. Soon afterwards, Moscow announced it would not retaliate against Obama’s sanctions.

When questioned by the FBI, Flynn lied about the nature of his conversations with Kislyak. He later pleaded guilty to one count of making false statements and agreed to co-operate with the Mueller investigation.

Paul Manafort

The veteran Washington lobbyist joined the Trump campaign team in March 2016 and served as the campaign manager between June and August 2016.

Manafort had a history of working for foreign leaders, including dictators Ferdinand Marcos and Mobutu Sese Seko.

In August 2018 he became the first member of the Trump campaign team to be found guilty by a jury.

Manafort was convicted of eight counts of tax and bank fraud. The jury were unable to reach a verdict on a further ten charges.

The charges relate to a period before Manafort joined the Trump campaign, when he made millions advising the pro-Russian Ukrainian leader Viktor Yanukovych.

On June 8 Manafort was charged with two additional counts relating to alleged witness tampering, along with his long-time aide Konstantin Kilimnik.

Manafort is due to stand trial for a second time in September.

Reports suggest Manafort was in debt to pro-Russian interests by up to $17m before he joined Trump’s campaign, although a spokesman issued a denial.

He attended the June 9, 2016 meeting at Trump Tower with Donald Trump Jr, Natalia Veselnitskaya and others.

Michael Cohen

The president’s former personal lawyer, fixer and occasional spokesman pleaded guilty to financial crimes in August 2018.

Cohen admitted organising payments to adult film actress Stormy Daniels and ex-Playboy model Karen McDougal after both women said they had affairs with Mr Trump, which he denies.

The lawyer said the payments were made “at the direction” of the then-presidential candidate to help influence the election.

Cohen’s attorney has said his client now wants to tell the “rest of the story” following the guilty pleas.

Cohen has already said that Donald Trump knew in advance about the meeting with Natalia Veselnitskaya in Trump Tower before the election, contradicting statements made by the president and his son Donald Jr.

The Christopher Steele dossier claimed that Cohen travelled to Prague for a secret meeting with Russian agents in August 2016.

But Cohen strongly denies this, and has even shown reporters his passport. It contained no Czech Republic stamp but did show the attorney had been in Italy – part of the Schengen border-free travel area – that summer.

Separate reports placed Cohen in a meeting with Felix Sater and Ukrainian politician Andrey Artemenko in New York in January 2017, where a Ukraine-Russia peace deal was discussed.

The New York Times claims Cohen told them he had personally delivered the proposal to Michael Flynn at the White House.

But Cohen disputed the story, telling CNN: “I acknowledge that the brief meeting took place, but emphatically deny discussing this topic or delivering any documents to the White House and/or General Flynn.”

Konstantin Kilimnik

Investigators have jointly charged Manafort and Konstantin Kilimnik with obstruction of justice and conspiracy to obstruct justice.

Kilimnik, who holds Russian and Ukrainian citizenship, had worked for Manafort as a translator and fixer since the early 2000s.

The indictment is the first time in the investigation that a Russian and American have been charged together.

Court documents allege that Manafort and Kilimnik tried to “corruptly persuade another person… with intent to influence, delay, and prevent the testimony of any person in an official proceeding”.

They are accused of contacting two lobbyists they had worked with while doing lucrative lobbying work for Viktor Yanukovych, and attempting to tamper with the evidence the lobbyists might give as potential witnesses in the investigation into Manafort’s work in Ukraine.

Investigators believe the lobbyists acted as intermediaries for Manafort and that he secretly hired a group of influential European politicians to quietly lobby US politicians and officials on behalf of Yanukovych’s government.

Multiple US news sources have identified Kilimnik as the “Person A” mentioned in previous court filings. Person A was assessed by the FBI as having ties to a Russian intelligence service at the time of the 2016 election and had such ties in 2016.

Alex van der Zwaan admitted to investigators that Rick Gates had told him Person A was “a former Russian Intelligence Officer” with the GRU, Russia’s main military foreign intelligence service.

Kilimnik’s current whereabouts are unknown, but he has previously been contacted by reporters and has denied any links to Russian intelligence.

Rick Gates

A former colleague of Paul Manafort and his deputy in the Trump campaign, he carried on working for Trump after Manafort resigned.

Gates was charged with multiple counts relating to the pair’s lobbying work for Ukraine.

In February 2018 he pleaded guilty to one count of making false statements to the FBI and one count of conspiracy against the United States.

The remaining charges against him were dropped after he entered the pleas and agreed to co-operate with the Mueller investigation.

Gates was the star witness in Paul Manafort’s trial in August 2018.

George Papadopoulos

Trump’s former foreign policy advisor has also admitted making false statements to the FBI.

Court documents say Papadopoulos lied about the timing of a meeting with a professor, who he understood to have “substantial connections” to Russian government officials.

According to court documents, the professor – later identified as Maltese academic Josef Mifsud – told Papadopoulos the Russians had “dirt” on Hillary Clinton, in the form of “thousands of emails”.

This conversation took place in April 2016, about a month after Papadopoulos had begun working for the Trump team.

The New York Times has reported Papadopoulos drunkenly passed on details of this conversation to Australian diplomat Alexander Downer. Australian officials then told their US counterparts, triggering the start of the FBI’s original Trump/Russia investigation.

After Papadopoulos’s guilty plea, Donald Trump tweeted: “Few people knew the young, low level volunteer named George, who has already proven to be a liar.”

The 13 Russians

In February the Justice Department charged 13 Russian citizens and three Russian companies with conspiring to interfere with the presidential election.

US prosecutors say the Russians began their operation in 2014. Their activities are said to include traveling to America on false pretences to collect intelligence, using the stolen identities of US citizens, and conducting “information warfare” on social media by using fake personas.

One of the companies is the Internet Research Agency, an organisation dubbed “the troll factory” over its reported efforts to spread misinformation on western social media sites.

In recent months Twitter and Facebook began notifying users who interacted with bots, trolls and propaganda from the St Petersburg-based company, commonly known as the “troll factory”.

The most high-profile of the 13 defendants is the Internet Research Agency’s alleged financial backer Yevgeny Prigozhin, a businessman with ties to Vladimir Putin.

Alex van der Zwaan

The London-based Dutch lawyer became the first person to be jailed as part of the Mueller inquiry.

Van der Zwaan, who is married to the daughter of Ukrainian-Russian billionaire German Khan, admitted lying to investigators about about his contact with Rick Gates.

The 33-year-old got a sentence of 30 days in prison after striking a deal with prosecutors in February, becoming the fourth person in the investigation to plead guilty to criminal charges.

Richard Pinedo

Pinedo is a US citizen from Santa Paula, California.

He pleaded guilty to identity fraud in February 2018 and has agreed to co-operate with investigators.

The charges, outlined in court papers, say Pinedo used the stolen identities of US citizens to create bank accounts.

He then sold the account numbers to people outside the country.

12 more Russians

Days before President Trump was due to meet Vladimir Putin for one-on-one talks in Helsinki, the Justice Department announced charges against 12 alleged members of Russia’s military intelligence agency, the GRU.

The charges represent the most detailed allegations heard yet over alleged Russian interference in the 2016 election campaign.

The 12 named Russian operatives are said to have hacked the Democrat party’s computer networks using a combination of fake “spearphishing” emails and sophisticated malware.

Court documents allege that the Russians began the hacking campaign in March 2016 at the latest. By April, they were planning to release material stolen from Democrat and Clinton campaign accounts.

They allegedly used the Guccifer 2.0 persona and set up the DCLeaks site to publish hacked emails, as well as co-ordinating with an unnamed “organisation that had previously posted documents stole from US persons, entities, and the US Government”.

The indictment does not mention Wikileaks by name and does not accuse anyone apart from the named Russians of criminality.

It alleges that they spearphished individuals affiliated with the Clinton campaign late on July 27, 2016, on the same day that Donald Trump said in a news conference: “Russia, if you’re listening, I hope you’re able to find the 30,000 emails that are missing.”

The 11-count indictment brings the total number of Russian citizens charged as part of the Mueller investigation to 25.

More on the arrests and charges:

President Donald J Trump

President Trump has repeatedly denied there was any collusion between his campaign and Russian actors, calling the Mueller investigation a “witch hunt”.

There has been widespread media speculation that Mueller is looking at whether Trump tried to obstruct justice by sacking his predecessor James Comey, or by pressuring Attorney General Jeff Sessions over the investigation.

Trump has said that he is “looking forward” to giving evidence to Mueller in person and under oath, but US media has speculated that the president’s lawyers are looking for ways to limit his legal risk. He could plead the fifth amendment and refuse to testify.

The president has also said he would consider it “a violation” for investigators to start looking into his family’s complex business interests, saying: “Look, this is about Russia.”

Donald Trump Jr

The president’s eldest child famously attended a meeting with Russian lawyer Natalia Veselnitskaya at Trump Tower in New York in June 2016. Jared Kushner and Paul Manafort were also there.

The meeting was arranged by Rob Goldstone, a British publicist working for Trump family friend Emin Agalarov.

In a statement released through his lawyer, Donald Jr initially said the meeting was about the adoption of Russian children.

But he later tweeted an exchange of emails he had with Goldstone, in which the Briton said Russian officials were offering to supply “documents and information that would incriminate Hillary [Clinton] and her dealings with Russia and would be very useful to your father”.

Goldstone added that the information “is part of Russia and its government’s support for Mr Trump”.

Donald Jr replied: “If it’s what you say I love it especially later in the summer.”

He later appeared before the Senate Judiciary Committee, the Senate Intelligence Committee and the House Intelligence Committee, giving evidence behind closed doors.

Trump Jr said he was skeptical about Goldstone’s offer of information on Hillary Clinton but felt he should hear him out.

He said the phrase “I love it” was “simply a colloquial way of saying I appreciated Rob’s gesture”.

The president’s son added: “I did not collude with any foreign government and do not know of anyone who did.”

The White House later admitted that the president had “weighed in” on the writing of his son’s initial statement, which made no mention of the offer of information on Clinton.

Jared Kushner

The Washington Post has alleged that Donald Trump’s son-in-law talked about setting up a secret channel of communication between the president-elect’s transition team and the Kremlin.

The conversation is said to have taken place in a meeting with Russian Ambassador Sergei Kisylak at Trump Tower, with Michael Flynn also in attendance, the newspaper said, citing US officials who had been briefed on intelligence reports.

Kushner says he and Flynn did sit down with the Russian diplomat in Trump Tower on December 1 2016, but denies claims of a secret back channel or any other wrongdoing.

In a statement to the Congressional committees, Kushner said he “stated our desire for a fresh start in relations” and asked about how to begin a dialogue after the vote.

He added: “The fact that I was asking about ways to start a dialogue after Election Day should of course be viewed as strong evidence that I was not aware of one that existed before Election Day.”

The Russian ambassador also arranged for Kushner to meet with Sergei Gorkov in December 2016. A graduate of the FSB state intelligence service academy, Gorkov is the head of Russian state investment bank Vnesheconombank.

Kushner said: “There were no specific policies discussed. We had no discussion about the sanctions imposed by the Obama Administration. At no time was there any discussion about my companies, business transactions, real estate projects, loans, banking arrangements or any private business of any kind.”

He added: “I did not suggest a ‘secret back channel’. I did not suggest an ongoing secret form of communication for then or for when the administration took office. I did not raise the possibility of using the embassy or any other Russian facility for any purpose other than this one possible conversation in the transition period. We did not discuss sanctions.”

Kushner said he met Ambassador Kislyak for the first time at a Trump foreign policy speech at the Mayflower Hotel in Washington in April 2016.

He said he merely shook hands and exchanged pleasantries with Kislyak.

Carter Page

Page is a former energy industry consultant with notably pro-Russian foreign policy views who joined the Trump campaign as a foreign policy advisor in 2016.

He has been on the radar of federal law enforcement since 2013, according to a memo released by Democrats on the House Intelligence Committee.

The memo says Page lived in Moscow from 2004 and 2007 and “pursued business deals with Russia’s state-owned energy company Gazprom”.

It appears to identify Page as a target for three Russian foreign intelligence agents charged by the US authorities in 2013 with trying to recruit US citizens as intelligence sources.

The memo says the FBI requested a Foreign Intelligence Surveillance Act (FISA) warrant in October 2016, shortly before the election, and renewed it three times. A FISA warrant allows the security agencies to eavesdrop on American citizens in national security cases.

Page has confirmed a 2013 meeting with Victor Podobnyy – who was later accused of conspiring with officers from Russia’s foreign intelligence service. Page has said he “shared basic immaterial information and publicly available research documents” with Podobnyy.

Conversations secretly recorded by the FBI suggest Page did not know the men were intelligence agents.

He was interviewed by the FBI about his Russian contacts in June 2013. Two months later, in a letter detailing his academic credentials, Page said: “Over the past half year, I have had the privilege to serve as an informal advisor to the staff of the Kremlin.”

In July 2016, Page flew to Moscow and gave a speech criticising US policy toward Russia.

The Christopher Steele dossier alleges that, while he was there, Page met with Igor Sechin, the head of energy giant Rosneft and a close ally of President Putin. Page has called this “absolutely ridiculous”.

Roger Stone

The colourful veteran Republican strategist cut his teeth working for disgraced former president Richard Nixon, before running a Washington lobbying firm alongside Paul Manafort.

Stone worked on the Trump election campaign in its early stages, but left in August 2015.

He sent tweets and made statements that appeared to anticipate the Wikileaks dump of John Podesta’s stolen emails.

Four days before Julian Assange’s organisation released the hacked messages, Stone tweeted: “I have total confidence that @wikileaks and my hero Julian Assange will educate the American people soon. #LockHerUp.”

Stone later revealed he had been exchanging direct messages with Guccifer 2.0, a Twitter user who the US intelligence community believe is a persona used by Russian intelligence to obscure its role in the hacking of Democratic emails.

Stone has called the conversation with Guccifer “meaningless” and denied having advanced knowledge of the Podesta leak. He says he only communicated with Wikileaks through an intermediary.

In a statement to the House Intelligence Committee, he said he had “no involvement” with “collusion with the Russian state to affect the outcome of the 2016 election”.

Felix Sater

Russian-born property developer with criminal convictions to his name and a history of helping US law enforcement.

Sater served time for assault after stabbing a man in the neck with the stem of a margarita glass in a bar fight in 1991.

In 1998 he was convicted of involvement in a fraud scheme run by the Russian mafia, but avoided prison by assisting the FBI and prosecutors.

In the 2000s, Sater acted as senior adviser to the Trump Organisation over the Trump SoHo hotel development in New York.

According to the New York Times, he sent Trump’s lawyer Michael Cohen a string of emails in November 2015 boasting about his contacts in the Kremlin.

One email suggests that building a Trump Tower in Moscow would boost Trump’s chances of winning the election, saying: “Our boy can become president of the USA and we can engineer it.” He added: “I will get all of Putins team to buy in on this, I will manage this process.”

Sater also reportedly attended the “peace deal” meeting with Cohen and a Ukrainian politician in New York in January 2017.

Steve Bannon

The former executive chairman of right-wing website Breitbart News served as the White House’s Chief Strategist for the first seven months of the Trump administration.

It emerged later that Bannon helped set up Cambridge Analytica, a UK-based company that used data from millions of Facebook users.

Cambridge Analytica claims it played it pivotal role in the US presidential election.

Bannon has admitted his involvement in the company but denied knowing anything about “the Facebook mining”.

Multiple reports said Bannon gave 20 hours of evidence to the Mueller investigation in February.

The writer Michael Wolff quoted Bannon as describing the Trump Tower meeting Donald Trump Junior, Jared Kushner, Paul Manafort and Russian Lawyer Natalia Veselntiskaya as “treasonous” and “unpatriotic”.

Bannon gave evidence to the Mueller investigation for around 20 hours, according to multiple reports, but only answered questions approved by the White House when called in front of the House Intelligence Committee.

Hope Hicks

The former model began working for Trump in 2014 and was promoted to White House communications director in September last year after the departure of Anthony Scaramucci after just 10 days in the job.

Hicks quit in February, a day after giving evidence for nine hours behind closed doors to the House intelligence committee.

She reportedly told the panel she had told occasional “white lies” on the President’s behalf, but denied lying about the Russia investigation.

More on the Trump circle:

Robert Mueller

Robert Swan Mueller III was director of the FBI under presidents George W Bush and Barack Obama, having started in the role just one week before 9/11.

Like President Trump, Mueller was born into a wealthy New York family and was privately educated.

He enlisted in the Marine Corps in 1968 and served as a combat soldier in the Vietnam War, winning Bronze Star and Purple Heart medals among others.

As a government prosecutor, he oversaw the prosecution of the Lockerbie bombing case and notorious Gambino family Mafia boss John Gotti.

In 2017, he was appointed as Special Counsel, tasked with investigating “any links and/or co-ordination between the Russian government and individuals associated with the campaign of President Donald Trump”.

Jeff Sessions

The Attorney General angered Trump after recusing himself from the Russia investigation.

Sessions had been forced to distance himself from the probe after he told US senators he had not been in in contact “with anyone connected to any part of the Russian government about the 2016 election”.

It emerged later that Sessions had in fact met ambassador Sergei Kislyak twice during the election campaign.

Sessions recused himself from any investigation into Russian interference in the presidential election, but said that this was not an admission of wrongdoing.

James Comey

Obama’s FBI Director played a controversial role in the 2016 election campaign.

He oversaw the FBI investigation into Hillary Clinton’s use of private email for official communications.

On July 5, 2016, the bureau said Clinton was “extremely careless” in handling emails, but said no charges would be filed against her.

However, on October 28, just days before the election, Comey told congress that the FBI had begun looking into newly discovered emails.

On November 6, just two days before the election, he announced that the bureau would not be changing its original decision not to charge Clinton.

Clinton herself, and some pollsters, said the decision to reopen the email investigation just before the vote had hurt her standing with voters.

The FBI had opened an investigation into connections between Russia and the Trump campaign in July 2016, but Comey did not make this fact public before the election.

Comey first met Trump in January 2017, when he briefed the president-elect on revelations in the Steele dossier.

Comey said a tense private dinner followed. He testified that Trump told him: “I need loyalty.” Comey said:

“I replied, ‘You will always get honesty from me.’ He paused and then said, “That’s what I want, honest loyalty.” I paused, and then said, “You will get that from me.”

Trump has flatly denied asking Comey for a pledge of loyalty, and also denies Comey’s claim that the president asked him to stop investigating Michael Flynn shortly after he sacked the national security adviser.

Trump fired Comey on May 9, 2017, initially saying that Attorney General Jeff Sessions and his deputy Rod Rosenstein had recommended his dismissal over Comey’s conduct in the Clinton email investigation.

But in an NBC interview, Trump said he was planning to sack Comey “regardless of recommendation”.

He added: “And in fact when I decided to just do it, I said to myself… this Russia thing with Trump and Russia is a made-up story.”

Devin Nunes

The Republican head of the House Intelligence Committee is a notable Trump loyalist who has attracted criticism for his role in investigating possible links with Russia.

Democrats called on Nunes to recuse himself from the House investigation into alleged Russian interference in the election in March last year.

That was after he went to the press with allegations that the Trump campaign team had been indirectly caught up in surveillance by US intelligence agencies.

Nunes’ claims chimed with Donald Trump’s tweets alleging that “Obama had my ‘wires tapped’ in Trump Tower just before the victory” – but did not prove the President right.

In February 2018 the Republican-controlled intelligence committee released a four-page memo prepared for Nunes by his staff, which alleged that the FBI used “politically motivated or questionable sources” to obtain the FISA warrant on Carter Page.

The claim rested on the allegation that Christopher Steele’s dossier, partly funded by the Clinton campaign, had “formed an essential part” of the FISA application – and this was not disclosed to the court when investigators made the application.

The White House approved the release despite objections from Democrat committee members and a written statement from the FBI expressing “grave concerns about material omissions of fact that fundamentally impact the memo’s accuracy”.

In response, Democrats on the committee prepared a rebuttal. A redacted version was released, which claimed that investigators “made only narrow use of information from Steele’s sources” when they asked for permission to put Page under surveillance.

John McCain

The veteran Republican senator and former presidential candidate has been one of President Trump’s staunchest critics.

McCain obtained Christopher Steele’s intelligence dossier via an intermediary – former British ambassador to Moscow Sir Andrew Wood.

McCain then passed it on to then-FBI director James Comey, saying: “I received the document, I looked at it, I thought that it ought to be seen by the proper authorities and I took it immediately over to Mr. Comey.”

Barack Obama

President Obama reportedly received a dossier of intelligence alleging Russian interference into the election in August 2016.

He met Putin in China in September, after the cyberattack against the Democratic National Convention, and said he said he the Russian president to “cut it out”.

In December 2016 Obama announced sanctions on Russia and ejected suspected intelligence operatives.

Both Democrats and Republicans have criticised the Obama administration for not being tougher on Russia.

In tweets, President Trump has variously asked why Obama “didn’t do something about Russia meddling” and why the previous administration started “an investigation into the Trump Campaign (with zero proof of wrongdoing) long before the Election in November? Wanted to discredit so Crooked H would win.”

Sally Yates

Yates was an Obama-era appointee who served as Acting Attorney General under Trump for just 10 days. But she played a major role in Michael Flynn’s downfall.

As the official temporarily in charge of the Department of Justice, Yates told the White House that Flynn had lied to colleagues about his contact with Russian ambassador Sergei Kislyak.

She said statements by Vice President Mike Pence in defence of Flynn did not square with what they knew Flynn had done.

Yates added: “The Russians also knew that General Flynn had misled the vice president and others because in the media accounts, it was clear from the vice president and others that they were repeating what General Flynn had told them.

“And that this was a problem because not only did we believe that the Russians knew this, but that they likely had proof of this information.

“And that created a compromise situation, a situation where the national security adviser essentially could be blackmailed by the Russians.”

Trump sacked Yates after she refused to defend his order restricting travel to the US from seven Muslim-majority countries.

John Podesta

Hillary Clinton’s campaign manager had his private Gmail account hacked in spear-phishing exploit in March 2016.

Wikileaks dumped thousands of the stolen emails online in October that year.

Private cybersecurity experts and the US government believe the Russian government was behind hacks of Democrat personnel.

Podesta later became the victim of “Pizzagate”, a bizarre conspiracy theory falsely alleging that words contained in the emails were code for child sex abuse.

Fake news stories about the Podestas and a Washington pizza restaurant were widely spread online, despite being comprehensively debunked.

More on the Washington players:

Vladimir Putin

The US intelligence community believes the Russian president personally ordered an influence campaign designed to undermine public faith in democracy and hurt Hillary Clinton’s chances of becoming US president.

Additionally, the Christopher Steele dossier claims that Putin personally endorsed a long-term plan to cultivate Trump as a way of encouraging splits and divisions in the West.

Putin and other senior Kremlin figures have dismissed the allegations in the dossier as a fabrication.

Sergey Kislyak

Russia’s ambassador to the US met with members of Trump’s circle, including Michael Flynn, Jared Kushner and Jeff Sessions, during the presidential campaign.

Flynn later pleaded guilty to lying about his contact with Kislyak.

And Kislyak later said the conversations with Flynn were “completely correct, calm, absolutely transparent,” adding: “In any case, there were no secrets on our side.”

Sessions agreed to recuse himself from the Trump/Russia investigation after it emerged he met the ambassador twice before the election, but failed to mention this when applying for his security clearance.

Kislyak was also present at the Oval Office meeting with President Trump and Russia’s Foreign Minister, Sergei Lavrov, in May 2017, when Washington Post reports allege that Trump disclosed classified intelligence on an Islamic State terror threat.

The president’s then- National Security Adviser, H R McMaster, said the newspaper’s account was wrong, saying: “At no time were any intelligence sources or methods discussed and no military operations were disclosed that were not already known publicly.”

Aras and Emin Agalarov

Aras Agalarov is an Azerbaijani-Russian property billionaire. His US-educated son Emin is a pop star in Azerbaijan and Russian.

The Agalarovs were photographed alongside Donald Trump when they hosted the 2013 Miss Universe competition in Moscow.

Emin performed during the beauty pageant – which was then jointly run by Trump – and Trump appeared in a cameo role in one of his music videos.

It was Emin’s publicist, Rob Goldstone, who set up the June 2016 Trump Tower meeting, between Kremlin-linked lawyer Natalia Veselnitskaya, Donald Trump Jr, Jared Kushner and others, after dangling the possibility of embarrassing material on Hillary Clinton.

Rob Goldstone

Former British journalist who worked as a publicist for Emin Agalarov.

Goldstone set up the meeting between Natalia Veselnitskaya and the Trump campaign at Trump Tower in June 2016.

Donald Trump Jr later released emails he exchanged with Goldstone before the meeting.

“Emin just called and asked me to contact you with something very interesting,” Goldstone wrote on June 3, 2016.

“The Crown prosecutor of Russia met with his father Aras this morning and in their meeting offered to provide the Trump campaign with some official documents and information that would incriminate Hillary and her dealings with Russia and would be very useful to your father.

“This is obviously very high level and sensitive information but is part of Russia and its government’s support for Mr. Trump – helped along by Aras and Emin.”

Donald Jr replied: “If it’s what you say I love it especially later in the summer.”

Responding to accusations of collusion between the Trump campaign and the Kremlin, Goldstone told the Sunday Times: “When people said that, I thought it was the most ridiculous thing I’ve ever heard. That doesn’t mean that maybe there wasn’t any Russian interference or Trump campaign collusion in other ways. I don’t know. But I’m sure I wasn’t part of it.”

He was interviewed behind closed doors by the House Intelligence Committee in December 2017.

Natalia Veselnitskaya

The lawyer and lobbyist was described as a “Russian government attorney” in Goldstone’s emails to Donald Jr, but she denies links to the Kremlin.

Veselnitskaya has campaigned against the Magnitsky Act – US sanctions legislation designed to punish Russian government officials linked to the death of anti-corruption whistleblower Sergei Magnitsky.

Both Kushner and Donald Trump Jr said they were disappointed with the meeting, stating that no research into Clinton was handed over. Donald Jr described it as “a wasted 20 minutes”.

Christopher Steele

The former MI6 Russia specialist was the author of an explosive independent dossier that claimed Russia held compromising information on Donald Trump.

Steele passed copies of his dossier to the FBI and John McCain through an intermediary.

He went into hiding after his identity was revealed by the Wall Street Journal.

Wikileaks

Julian Assange’s group released nearly 20,000 emails that had been stolen from the Democratic National Convention (DNC) on July 22, 2016.

And in October and November 2016, Wikileaks published more than 58,000 messages from Hillary Clinton’s campaign chief John Podesta.

The US intelligence community claims that Wikileaks played a key role in helping a Russian cyber campaign, accusing the group of collaborating with Russian state media in the past.

An ex-Wikileaks employee leaked direct messages apparently sent by Assange in November 2015 in which he called Clinton a “sociopath” and said: “We believe it would be much better for GOP to win.”

Assange has denied sending the messages and repeatedly said Russia was not the source of the hacked emails.

The Hackers

So who actually hacked the Democrats in the first place? That’s still a matter of debate.

In June 2016 the private security firm Crowdstrike claimed that Cozy Bear and Fancy Bear, two hacking operations allegedly backed by Russia, were the culprits.

Shortly after, an individual using the name Guccifer 2.0 claimed responsibility, publishing documents apparently stolen from the DNC to back up the claim.

Guccifer 2.0 said he was Romanian and not connected to Russia, although a report claims that metadata shows the individual was familiar with the Russian language.

The US intelligence community believes their Russian counterparts used the Guccifer 2.0 persona, Wikileaks and a site called DCLeaks “to release US victim data obtained in cyber operations”.

However, a number of former US intelligence operatives, including NSA official-turned-whistleblower William Binney, believe DNC data was copied – rather than remotely hacked – because it was transferred “at a speed that far exceeds an Internet capability for a remote hack”.

The implication some have drawn from this is that it could have been an inside job by the DNC.

This claim has gained traction; reports say that President Trump even urged the CIA Director Mike Pompeo to meet Binney.

But the claims are highly disputed, with many experts dismissing them as conspiracy theories. One former CIA officer told The Intercept it was “like coming out with the theory that the Japanese didn’t bomb Pearl Harbor.”

Detailed technical analyses of the claim have highlighted flaws and say it jumps to conclusions. For instance, experts say it does not take into account the possibility that the data had already been hacked, and was copied and transferred later.

Donald Trump’s position on the identity of the culprits has shifted.

In June 2016 he released a statement saying: “We believe it was the DNC that did the ‘hacking’ as a way to distract from the many issues facing their deeply flawed candidate and failed party leader.”

In July, a few days after the first Wikileaks release, he famously said in a press conference: “Russia, if you’re listening, I hope you’re able to find the 30,000 emails that are missing.”

But, after that, Trump repeatedly cast doubt on the Russian hacking theory, disagreeing with the assessment of America’s intelligence agencies even after he won the election.

By 2017, he appeared to grudgingly accept evidence of Moscow’s involvement, saying: “As far as hacking, I think it was Russia. But I think we also get hacked by other countries and other people.”

Cambridge Analytica

The British data firm claims it ran key parts of Donald Trump’s election campaign.

Investigations by Channel 4 News and others revealed how Cambridge Analytica harvested data that came from around 50 million Facebook profiles, allowing it to micro-target its messaging on social media.

Speaking about Trump’s campaign, the company’s CEO Alexander Nix told an undercover reporter: “We did all the research, all the data, all the analytics, all the targeting, we ran all the digital campaign, the television campaign, and our data informed all the strategy.”

Another senior executive described how the company created the “Defeat Crooked Hillary” brand of attack ads, used against Clinton during the campaign.

The company has since denied using the Facebook data in the Trump campaign or the US presidential election.

Steve Bannon was vice president of the company until 2016, when he left to become head of the Trump campaign.

And billionaire Robert Mercer, who had already invested millions in Cambridge Analytica, injected a huge amount of cash into Trump’s campaign in 2016.

SCL Group, Cambridge Analytica’s parent company, said it had signed an agreement with Donald Trump’s former National Security Advisor Michael Flynn about possible advisory work a week before the presidential election in November, 2016, but said it never actually hired Flynn.

Responding to the investigation by Channel 4 News, Cambridge Analytica said it “has never claimed it won the election for President Trump”, adding that it is committed to assisting the Mueller investigation. “CA is not under investigation, and there is no suggestion of any wrongdoing by the company,” it said.

Josef Mifsud

The Maltese academic was quickly identified as the initially unnamed “professor” who met Trump aide George Papadopolous in March 2016.

Court papers alleged that Papadopolous met the London-based professor after being promised “dirt” on Hillary Clinton in the form of “thousands of emails”.

The same papers suggest Papadopolous talked down Mifsud’s credentials to investigators, despite knowing he “had substantial connections to Russian government officials (and had met with some of those officials in Moscow immediately prior to telling defendant Papadopoulos about the “thousands of emails”)”.

Mifsud – who had been employed by universities of Stirling and East Anglia – admitted being “the professor” but denied any wrongdoing when contacted by the Daily Telegraph, saying he had a “clear conscience”.

More on the foreign actors:

What exactly is Mueller investigating?

“Any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump, and any matters that arose or may arise directly from the investigation.”

In practice, Mueller is seeking to answer a number of distinct questions:

Did Russia interfere with the 2016 election?

This includes probing alleged so-called “active measures” carried out by the Russian state, including using the Internet Research Agency to target voters with false information.

In recent months Twitter and Facebook began notifying users who interacted with bots, trolls and propaganda from the St Petersburg-based company, commonly known as the “troll factory”.

The Mueller probe will also be looking into well-publicised hacks of the Democratic National Committee computer network, and the personal emails of Clinton campaign chairman John Podesta.

Were these cyber exploits carried out at the request of Russian intelligence, with a view to embarrassing the Clinton campaign?

Did Trump’s team collude with Russia?

There’s no dispute that members of the Trump team came into contact with Russians during the election campaign and afterwards, but “collusion” in the sense of actively working with Russia to influence the outcome of the vote is strongly denied.

Trump’s former National Security Advisor Michael Flynn has admitted he lied about contact he had with the Russian embassy and senior members of the Trump transition team.

And the president’s son, Donald Jr, was personally promised information about Hillary Clinton, which was clearly stated to come from the Russian government. He released messages showing that he responded, saying:”If it’s what you say I love it…”

Trump Jr has also admitted going to a meeting at Trump Tower on June 9, 2016 with Natalia Veselnitskaya, a Russian lawyer alleged to have links to the Kremlin.

Trump’s then-campaign chairman Paul Manafort and the president’s son-in-law Jared Kushner were also at the meeting.

Did Americans launder Russian money?

Manafort and a colleague, Rick Gates, have both been charged with conspiracy to launder money. Manafort denies all wrongdoing and the charges against Gates were dropped following his plea bargain.

The charges we know about related to a period of time before Manafort became involved in the Trump campaign, and the president’s team has consistently denied there is a connection.

Did Trump try to obstruct justice?

Some legal commentators think Trump is vulnerable to accusations that he tried to obstruct justice by allegedly derailing the FBI investigation.

Trump fired James Comey – the man who led the probe before Mueller – and then gave conflicting reasons why.

Reports say the president also tried to stop Attorney General Jeff Sessions from recusing himself from the Russia investigation, suggesting the president expected his officials to protect him from the probe.

More in-depth reports from Channel 4 News