The resignation of CIA chief David Petraeus has provoked a wave of speculation in Washington over the timing and the nature of his departure.

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

Petraeus - a four-star general who was universally admired, even revered, for his achievements in Iraq and Afghanistan - might have survived a sex scandal, were it not for the controversy already surrounding the CIA.

He was due to address a Senate hearing next week into the agency's response to the terror attack in Benghazi, when US ambassador Christopher Stevens and three other US diplomats were killed.

Many on the right have questioned whether the timing of his departure was linked to the scandal: like Rupert Murdoch, who tweeted "Petraeus resignation. Timing, everything suspicious. There has to be more to this story."

Some in the administration have openly questioned intelligence statements in the immediate aftermath: now it will be up to Petraeus' successor, Michael Morell, to appear before the Senate in his place.

And this is just the latest in a series of embarassing sex scandals: Obama's choice for US ambassador to Iraq , Brett McGurk, withdrew his name after some racy emails were leaked online revealing that he had an extra-martial affair with a Wall Street Journal reporter in 2008, when both were stationed in Iraq.

Back in April, it emerged that members of an advance security team in Colombia had been involved with prostitutes, ahead of a visit by President Obama.

Leading Democratic senator Dianne Feinstein thought Petraeus should have been allowed to stay on: "I wish President Obama had not accepted this resignation, but I understand and respect the decision", she said.

But according to reports, the affair was exposed after an FBI investigation was launched into whether a woman had had access to the general's personal gmail account. That woman is believed to be Paula Broadwell, author of a highly flattering autobiography about Petraeus, entitled "All In."

Broadwell, whose own website was taken offline on Friday, has not been available for comment. A graduate of Harvard as well as the West Point military academy, she was embedded as a journalist with Petraeus's team in Afghanistan , and frequently went on five-mile runs with him.

A self-styled "soccer mom", she is also an ironman triathlete, and a model for a machine-gun manufacturer.

"My wife's lover"

Blake Houndsell, from Foreign Policy magazine, has suggested that her husband could have hinted at the affair months ago. He posted a link to an anonymous letter to a New York Times advice column, The Ethicist, entitled "My Wife's Lover".

The author describes an affair his wife is having with "a government executive" who is managing "a project seen worldwide as a demonstration of American leadership."

"Exposing the affair will create a major distraction that would adversely impact the success of an important effort", the writer goes on, before wondering whether he should suffer in silence for the sake of the greater good.

Not neccessarily, suggests the reply. "I halfway suspect you're writing because you want specific people to read this column and deduce who is involved."

Smoke and mirrors

Complete coinicidence? Maybe. But in the shadowy world of smoke and mirrors that surrounds the intelligence community, it's the kind of theory that is bound to find traction, true or not.

But there are more serious issues at stake than a sex scandal. Martha Raddatz, from ABC News, reported that people who knew Petraeus had been receiving anonymous emails, which were then traced to Broadwell, which triggered the FBI investigation.

As the Wall Street Journal comments: "Security officials are sensitive to misuse of personal email accounts - not only official accounts - because there have been multiple instances of foreign hackers targeting personal emails."

Michael Morell, who ran the CIA for two months before Petraeus took over, will take charge for the meantime, and could well become the permanent successor. He already has three decades of experience and has been described as "the consummate straight shooter" who "projects an image of calm".

But for Petraeus the damage is incalculable, and the US has now lost one of its most talented and widely respected public officials. Conspiracy theories notwithstanding, it simply was not the moment to ride out a political storm.

Felicity Spector writes about US politics for Channel 4 News