The author of a controversial book on Donald Trump's White House says the US president has "less credibility than perhaps anybody who has ever walked on Earth at this point".
Michael Wolff, who spent months in Mr Trump's White House while researching the book, was responding to Mr Trump's claims that it was "full of lies".
Mr Trump's lawyers had tried to block publication of Fire and Fury: Inside the Trump White House.
The book has now gone on sale early.
Mr Wolff told NBC's Today show that Mr Trump's staff "all say he is like a child".
He added: "What they mean by that is he has the need for instant 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 book 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".
It also portrays Mr Trump as being surprised by winning the presidency.
Mr 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.
Asked about those – including Mr Trump himself – who had questioned the veracity and accuracy of his accounts of a tumultuous year in the White House, he said he "absolutely" stood by everything he had written.
Mr Trump said he had not given Mr Wolff access to the White House nor spoken to him for the book.
Mr 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."
Asked if attempts to block the book's publication, and the attendant publicity, had helped sales, he smiled and said: "Where do I send the box of chocolates?"
What's in the book?
Mr Wolff's book makes many claims, including that:
- The Trump team was shocked and horrified by his election win
- His wife, Melania, was in tears of sadness on election night
- Mr Trump was angry that A-list stars had snubbed his inauguration
- The new president "found the White House to be vexing and even a little scary"
- His daughter, Ivanka, had a plan with her husband, Jared Kushner, that she would be "the first woman president"
- Ivanka Trump mocked her dad's "comb-over" hairstyle and "often described the mechanics behind it to friends"
The book is reportedly based on more than 200 interviews but some excerpts have been criticised and questioned.
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.
One of the key claims is about the Trump Tower meeting. Mr Bannon is quoted in the book as saying about it: "They're going to crack Don Junior like an egg on national TV."
The meeting is being investigated by Special Counsel Robert Mueller as part of his inquiry into possible collusion between Trump campaign officials and Russians.
Mr Trump strongly denies any collusion took place.
What's been the reaction?
Mr Trump said the book was "full of lies, misrepresentations and sources that don't exist".
I authorized Zero access to White House (actually turned him down many times) for author of phony book! I never spoke to him for book. Full of lies, misrepresentations and sources that don’t exist. Look at this guy’s past and watch what happens to him and Sloppy Steve!
— Donald J. Trump (@realDonaldTrump) January 5, 2018
End of Twitter post by @realDonaldTrump
He also said Mr Bannon – who was sacked in August – had "lost his mind" after losing his White House position.
On his Breitbart radio show on Wednesday, Mr Bannon responded to the president's criticism by saying Mr Trump was a "great man" and that he supported him "day in and day out".
On Thursday a reporter asked Mr Trump if his former strategist had betrayed him.
"I don't know, he called me a great man last night so he obviously changed his tune pretty quick," the US leader responded.
In other reaction:
- A spokesperson for Melania Trump said she had encouraged her husband's presidential bid and was happy he won
- White House press secretary Sarah Sanders dismissed the book as a "trashy tabloid fiction" that she said was "filled with false and misleading accounts"
- The White House said it was banning personal devices, including mobile phones, from the West Wing, citing security concerns.
What did Mr Trump's lawyers argue?
The legal notice has been published by the Washington Post. It demands that Mr Wolff and the book's publisher "immediately cease and desist from any further publication, release or dissemination of the book".
It accused Mr Wolff of making "numerous false and/or baseless statements" about Mr Trump and said lawyers were considering pursuing libel charges.
Attorney Charles J Harder also sent a cease-and-desist letter to Mr Bannon on Wednesday, saying he had violated a non-disclosure agreement.
The book was due to come out next Tuesday but publication was advanced following the legal moves.