Binyamin Netanyahu appeals to the US congress to reject a nuclear deal with Iran that Barack Obama is hoping to strike. Where does that leave US-Israeli relations?
Iran says its nuclear programme is peaceful and is designed for electricity generation, but its critics believe it is trying to develop weapons.
The US and Iran are in the midst of delicate negotiations that Washington hopes will lead to the programme being halted in return for relief from economic sanctions. This would need to be verifiable to satisfy the Americans.
President Obama wants Iran to hold back for at least 10 years so a deal can be agreed with the US, UK, France, Germany, Russia and China by 31 March, the deadline for an interim agreement (with a final agreement by 30 June).
He is not optimistic a final deal will be achieved, but argues that jaw jaw is better than war war, that negotiations have a better chance of success than military action or sanctions.
Israel does not accept Iran’s intentions are peaceful, and is concerned it will use its civil nuclear programme for military purposes – threatening the Jewish state.
Israel, a nuclear weapons state, is worried about the Iranian-backed Hezbollah, with whom it fought a war in Lebanon in 2006.
Prime Minister Netanyahu’s supporters say he is not being paranoid – after all, former Iranian president Mahmoud Ahmadinejad declared that Israel should be “wiped off the map”.
But there appears to be a disagreement between Netanyahu and the Israeli intelligence service, Mossad, over how advanced Iran’s programme is.
During his trip to Washington, Mr Netanyahu will not be meeting President Obama, who believes he was wrong to oppose an interim nuclear deal agreed in 2014.
The president says Iran has not developed its programme since then, and that Netanyahu’s scepticism is unfounded.
The Israeli prime minister was invited to Washington by Republican House Speaker John Boehner, against Obama’s wishes, and is making a speech to congress on Tuesday.
He told the American Israel Public Affairs Committee (Aipac) on Monday (pictured above) that he had a “moral obligation” to warn about the dangers of a nuclear Iran.
Some leading Republicans and Democrats sympathise with his position, but the US administration is adamant that the talks with Iran must not be jeapordised.
Netanyahu no doubt believes what he says, but he is also contesting elections in a fortnight and hopes that “standing up” for Israel will prove a vote winner.
When he last spoke to both houses of congress, he received a series of standing ovations and expects a similar reception this time. This would infuriate Netanyahu’s political opponents, who believe he is electioneering rather than representing Israel abroad.
While being wary of Iran, they also question his decision to take on Obama in such a brazen manner. For his part, Netanyahu sees parallels between Europe’s appeasement of Hitler in the 1930s and the Iran negotiations.
By appearing to question Obama’s judgement in his speech, he could be accused of intervening in US politics on the side of the president’s Republican oponents.
Read Lindsey Hilsum: why Netanyahu wants to scupper a US deal with Iran
Until 2007, Israel received economic aid from the US. Since then, assistance has come in the form of military aid (currently worth $3bn a year, most of which has to be spent on American defence equipment).
The two countries also share military intelligence and America pays for the iron dome missile shield, developed by Israel at its own expense, that helped to protect it when Hamas rockets were fired from Gaza in the 2014 war.
But the ties between them go further than that. The US views Israel as a democracy in an unstable region that needs protection against existential threats.
Jewish-American charities and individuals raise money for Israel and Aipac provides a sympathetic ear and can be relied on to argue the Israeli case.
The US also provides Israel with diplomatic support at the UN, using its security council veto when it believes the country’s interests are threatened.
Obama and Netanyahu do not get on, and while the close relationship that has been built up between the two countries over several decades is not going to disintegrate because of this, it is always better for countries if their leaders manage to establish a good rapport with the US president.
A basic rule of thumb for diplomacy is that if you are going to choose a foreign leader to fall out with, best this is not the leader of the most powerful country in the world.
By appealing over Obama’s head to senior politicians in the US, Netanyahu can only worsen his already strained relationship with the US president.
The words he uses in his speech to congress must be carefully chosen: he has more to lose than Obama if they create more antagonism between the two administrations.
Yes, arguments between the two countries are not unprecedented. During the 1956 Suez crisis, the US intervened to force Israel – and Britain and France – to withdraw from Egypt.
George Bush Snr had a disagreement with Israel in 1991 when he said east Jerusalem was occupied territory, not a sovereign part of Israel. His secretary of state James Baker criticised Israel’s “expansionist policies” at the time, a theme taken up by Bill Clinton a few years later while talking about Jewish settlements in the West Bank.
Under George Bush Jnr’s presidency, the US was critical of Israel’s assassination of suspected terrorists.
Obama was said to be “livid” when Israel announced during a visit by Vice-President Joe Biden (pictured above) in 2010 that hundreds of new homes would be built in east Jerusalem – while the US was pushing for a peace deal between Israel and the Palestinians.
It was not to be the last time that Obama and Netanyahu fell out.