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US President Donald Trump. Image Credit: AP

In an extraordinary and unprecedented public defence of his own mental stability, Donald Trump has issued a volley of tweets that seemed guaranteed to add fuel to a growing constitutional crisis.

Suggestions that he was mentally unfit to be president were out of "the old Ronald Reagan playbook", Trump wrote on Saturday.

"Actually," the president added , "throughout my life, my two greatest assets have been mental stability and being, like, really smart."

He also said he " went from VERY successful businessman , to top T.V. Star .... to President of the United States (on my first try). I think that would qualify as not smart, but genius ... and a very stable genius at that!"

The author of the book that precipitated a week of fierce and growing debate over Trump's fitness to be president, Fire and Fury: Inside the Trump White House , had earlier told the BBC: "I think one of the interesting effects of the book so far is a very clear emperor has no clothes effect."

Michael Wolff's book burst into the public consciousness on Wednesday, when the Guardian published excerpts nearly a week ahead of its planned publication . In the ensuing political firestorm, Trump threatened to sue the journalist and former Guardian columnist but succeeded only in prompting his publisher, Henry Holt, to bring the book forward .

Speaking to the BBC, Wolff added: "The story that I have told seems to present this presidency in such a way that it says he can't do his job.

"Suddenly everywhere people are going, 'Oh my God, it's true, he has no clothes'. That's the background to the perception and the understanding that will finally end ... this presidency."

The 25th amendment of the US constitution provides for the removal of a president deemed unfit to fulfil his role if a majority of the cabinet and the vice-president agree. Talk of such a path to removing Trump from power has increased with the publication of Wolff's book.

Bandy Lee, an assistant clinical professor at the Yale school of medicine, briefed a dozen members of Congress, mostly Democrats, last month on the potential risks associated with Trump's behaviour.

At the end of a week that began with Trump taunting North Korea over the size of his " nuclear button ", Lee, whose career has centred on studying, predicting and preventing violence, told the Guardian she and other psychiatrists were speaking out because they felt "the danger has become imminent".

Trump was at the presidential retreat Camp David on Saturday for a policy weekend with Republican congressional leaders . He first tweeted remarks about unemployment figures and an ABC journalist who was suspended for a mistake in reporting about the president and Russian interference in the 2016 election.

Not long after 7am local time, the president wrote : "Now that Russian collusion, after one year of intense study, has proven to be a total hoax on the American public, the Democrats and their lapdogs, the Fake News Mainstream Media, are taking out the old Ronald Reagan playbook and screaming mental stability and intelligence...

"...Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart. Crooked Hillary Clinton also played these cards very hard and, as everyone knows, went down in flames. I went from VERY successful businessman, to top T.V. Star...

"...to President of the United States (on my first try). I think that would qualify as not smart, but genius ... and a very stable genius at that!"

Wolff's book hit the stores on Friday, prompting queues and a rush that put it top of the Amazon sales charts.

White House on Wolff's book

The White House has forcefully criticised Wolff's book and questioned the author's integrity. Wolff has said he stands by his work, which included more than 200 interviews and was built on extensive access to the West Wing and key figures within it.

On Friday night Trump hit out at Wolff - tweeting that he was "a total loser who made up stories in order to sell this really boring and untruthful book" - and Steve Bannon, his former campaign chief executive and White House strategist who is a major source for the volume.

Wolff "used Sloppy Steve Bannon, who cried when he got fired and begged for his job" the president wrote. "Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad!"

Bannon has avoided extensive comment on the affair, though in the immediate aftermath of the Guardian's publication of excerpts of Wolff's book he called Trump "a great man". The billionaire Rebekah Mercer, a key backer, has disowned him and his role at the far-right Breitbart News is believed to be under pressure.

Trump's reference to "the Ronald Reagan playbook" was a curious one. Reagan was formally diagnosed with Alzheimer's, a degenerative brain disease, in 1994, five years after he left office.

The extent to which he suffered during his time in the White House, when the cold war was still current, remains a matter of contention even within his own family.

Reagan, who like Trump was in his 70s when in office, long faced questions over his mental state. Opponents pointed to his habit of forgetting names and making contradictory statements.

In a column for the Hollywood Reporter this week, Wolff wrote of Trump: "Everybody was painfully aware of the increasing pace of his repetitions. It used to be inside of 30 minutes he'd repeat, word-for-word and expression-for-expression, the same three stories - now it was within 10 minutes. Indeed, many of his tweets were the product of his repetitions - he just couldn't stop saying something."