Bolton went on to tell The Washington Post's Robert Costa: "Let's be clear, I resigned, having offered to do so last night." Pressed further, he said, "I will have my say in due course. But I have given you the facts on the resignation. My sole concern is US national security."

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Bolton, who is apparently already talking to several media outlets, offered a fuller and more direct contradiction to The Daily Beast. After it quoted White House press secretary Stephanie Grisham, who backed up Trump's account, Bolton responded in a text: "[White House] press secretary statement is flatly incorrect."

Those statements don't necessarily add up to a complete contradiction of what Trump said, but they are entirely suggestive of one. Trump implied he initiated the resignation, but Bolton says he offered it.

Bolton also suggests Trump didn't make a final determination on Monday night, even as Trump claims he had already decided and made the request.

The plot thickens as you look at Bolton's previous tweets.

On Monday night and again on Tuesday morning, Bolton tweeted remembrances of September 11th.

That could simply be because this week is the 18th anniversary of the attacks. But they could also be read to suggest discord with Trump over the president's aborted plans to meet with the Taliban at Camp David.

Trump announced this weekend that he cancelled the secret planned meeting after 12 people, including an American, were killed in Afghanistan. Bolton is extremely hawkish on foreign policy and has generally abhorred negotiating with antagonistic foreign leaders. The Washington Post has reported that Bolton has been fighting against the negotiations, while Pompeo has been supportive of them.

Bolton has reason to argue that he resigned rather than that he was effectively fired - most notably, for his own personal pride.

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But it's highly unusual for former aides to so directly challenge Trump upon their departure, with the notable exception of former veterans affairs secretary David Shulkin, who maintained that Trump fired him rather than that he resigned.

Even when departed aides have left Trump's White House or Cabinet on bad terms, they have generally been wary of even the perception of criticising the president.

Former defence secretary Jim Mattis, for instance, resigned in protest over Trump's later-aborted plan to completely withdraw from Syria. But even on a recent book tour, he has declined to disagree directly with Trump.

Bolton, though, has always been extremely outspoken about his foreign policy, rarely shying away from taking unpopular positions.

In contrast to the growing number of yes-men and -women who surround Trump, he's a true believer who logic suggests could ruffle some feathers in the weeks and months ahead - particularly if he views Trump as capitulating to America's enemies.

A source close to Bolton was talking in the White House shortly after the news broke, playing up the idea that he had prevented "bad deals" from being made with the likes of the Taliban, North Korea and Iran, according to CNBC reporter Eamon Javers, writing on Twitter.

It will be a fascinating dynamic, judging by Bolton's willingness to engage on the matter in less than an hour after his departure was tweeted.

The Washington Post