The author of a controversial book on Donald Trump says that all his White House aides see him as a "child" but the accuracy of the book has been questioned in the US media.
Michael Wolff said his book was based on about 200 interviews, and rejected Mr Trump's claims that it was "phony" and "full of lies".
The president said he never spoke to him but Wolff told NBC's Today show that they spent three hours together.
The book has now gone on sale early despite Mr Trump's attempts to stop it.
Fire and Fury: Inside the Trump White House, paints a withering picture of Mr Trump as inept, sexist, narcissistic, even semiliterate, and the White House as dysfunctional and chaotic under his presidency.
The book also cites former top aide Steve Bannon as describing a meeting at Trump Tower in New York between a Russian lawyer and Trump election campaign officials, including Mr Trump's son Donald Jr, as "treasonous".
Both Mr Trump Jr and his father deny that any collusion with Russians to win the election took place. The meeting is being investigated by Special Counsel Robert Mueller as part of his inquiry into possible collusion between Trump campaign officials and Russians.
Wolff said that White House staff described the president as childlike because "he has the need for immediate gratification. It's all about him... This man does not read, does not listen. He's like a pinball just shooting off the sides."
The president said he had not given Wolff access to the White House nor spoken to him for the book.
But Wolff responded: "What was I doing there if he didn't want me to be there? I absolutely spoke to the president... It was not off the record."
He said he had spent three hours with Mr Trump in total, both during the election campaign and after the inauguration.
Hitting back in the television interview Wolff said the president had no credibility and that "100 percent of the people around him" question his fitness for office.
Wolff said it was "extraordinary" that the president of the US would try to stop publication of his book, a move that "the CEO of a mid-sized company" would not attempt.
Wolff's credibility questioned
The accuracy of some excerpts has been criticised and questioned in the US media.
The Washington Post said Mr Wolff had past form for "not just recreating scenes in his books and columns, but of creating them wholesale".
"As he recounted in Burn Rate - his best-selling book about his time as an early Internet entrepreneur - Wolff kept his bankers at bay by fabricating a story about his father-in-law having open-heart surgery," the newspaper writes.
Likewise, a 2004 profile of Mr Wolff in New Republic made a similar accusation, saying that his writing sprang "from Wolff's imagination rather than from actual knowledge of events".
That same profile effectively dismissed Mr Wolff as a columnist who, while "entertaining and a superb writer", was more interested in "atmosphere and gossip" than conventional reporting.
"His prose is a whirlwind of flourishes and tangents and asides that often stray so far from the central point that you begin to wonder whether there is a central point," it wrote.
"His great gift is the appearance of intimate access," an editor who has worked with Mr Wolff said.
"He is adroit at making the reader think that he has spent hours and days with his subject, when in fact he may have spent no time at all."
In 2014, The Guardian abruptly cancelled a weekly column by Mr Wolff, without explanation, saying only that it was "time to go our separate ways".
More and more political figures are questioning the book's accuracy.
Former UK prime minister Tony Blair has also denied an allegation that he personally warned Mr Trump's son-in-law that British agents may have spied on him during the 2016 US election.
"This story is a complete fabrication, I mean literally from beginning to end," Mr Blair said.
"I've never had such a conversation in the White House, outside of the White House, with Jared Kushner, with anybody else.
"It's sort of a reflection to me on the crazy state of modern politics. I mean, here's a story that's literally an invention that is now halfway around the world with conspiracy theories attached to it."
Former White House press secretary Sean Spicer has denied Mr Wolff's claim - revealed in an excerpt published in New York Magazine - that on election night Mr Trump had "looked like a ghost" and his wife "Melania was in tears - and not of joy".
"The idea that she was crying is nonsense," Mr Spicer told CNN.
"Melania Trump was the one who encouraged President Trump to run for office. She was very supportive of this."
"If 10 percent [of the book] isn't true, 20 percent isn't true, 30 percent - what is the reader supposed to guess? What is accurate and what isn't?" he said.
Still, even if only half of what the book contains is true, it paints a damning portrait of a paranoid president and a chaotic White House, BBC North America editor Jon Sopel says.
- BBC / ABC