US President Donald Trump has labelled author Michael Wolff a "total loser"
The author of a controversial book that is highly critical of Donald Trump's first year in the White House has claimed his revelations will eventually "bring down" the US President.
Michael Wolff made the claim in an interview with the BBC, responding Mr Trump's description of his book as "boring and untruthful."
Fire and Fury: Inside The Trump White House quotes aides as saying Mr Trump has a short attention span, often repeats himself and refuses to read briefing notes.
Mr Wolff told BBC radio that "one of the interesting effects of the book so far is a very clear emperor-has-no-clothes effect."
Speaking on Radio 4, he 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."
Mr Wolff has said he wrote the book after conducting about 200 interviews.
Meanwhile President Trump has unleashed a Twitter tirade against Mr Wolff, labelling him a "total loser who made up stories in order to sell this really boring and untruthful book."
"He used Sloppy Steve Bannon, who cried when he got fired and begged for his job.
"Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad!"
The spat has only served to heighten demand for the book - with people queuing round the block for a copy.
The book – ‘Fire and Fury’ - quotes White House aides claiming Mr Trump has a short attention span, often repeats himself and refuses to read briefing notes.
Mr Wolff said many of those close to the president describe him as a "moron," an "idiot" and "like a child."
Yesterday, he told NBC News Today what White House staff think of President Trump:
"They all say he is like a child,” he said.
"And what they mean by that is he has a need for immediate gratification. It's all about him; they say he is a moron; an idiot."
Wolff claims Mr Trump's former ally and chief strategist Steve Bannon questioned his fitness for office.
Mr Bannon was sacked by Mr Trump in August.
Meanwhile, US Secretary of State Rex Tillerson has defended President Trump's mental fitness, responding to claims in the book.
In an interview with CNN, Mr Tillerson said: "I've never questioned his mental fitness. I've had no reason to question his mental fitness.”
"He is not a typical President of the past, I think that's well-recognised. That's also why the American people chose him."
The relationship between Mr Tillerson, a former oil executive, and Mr Trump has not always been strong but, in response to rumours he may be shown the door, Mr Tillerson said: "I intend to be here for the whole year."
Last year, he reportedly described the President as a "moron" after a national security meeting, a claim denied by his office.
According to the book, the President is regarded as an "idiot" by treasury secretary Steve Mnuchin and former chief of staff Reince Priebus.
President Trump has described the book as "phony" and "full of lies".
Mr Trump's lawyers tried to block publication of the book, before publishers brought the release date forward.
Presidential historian Doug Brinkley has said the claims in the book are unprecedented:
“We have had people from inside the White House get fired or leave and write a disgruntled memoir but this is one after the other,” he said.
“It is a beehive of stings that Donald Trump is taking from Wolff here.
“And that Steve Bannon turned on his friend and boss Donald Trump so quickly.”
Wolff also says President Trump, 71, did not want to win the 2016 presidential election because losing would offer "a far more powerful brand and untold opportunities."
But Press Secretary Sarah Huckabee Sanders said this was "ridiculous," adding that President Trump and his family "would not have put themselves through" the campaign if they did not want to win.
Wolff said he spoke to Mr Trump after his inauguration and "spent about three hours with the President over the course of the campaign in the White House, so my window into Donald Trump is pretty significant."
He added: "I spoke to people who spoke to the President on a daily, sometimes minute-by-minute basis."