First, Trump issued a remarkable personal statement denouncing Steve Bannon, his one-time confidant, whom he castigated as self-aggrandising and not a critical figure.

“Steve Bannon has nothing to do with me or my presidency,” Trump said. “When he was fired, he not only lost his job, he lost his mind.”

The White House spokeswoman Sarah Sanders said the president was “furious and disgusted” at Bannon’s attacks on his family, which included the claim that Donald Trump Jr’s Trump Tower meeting with a group of Russians who promised dirt on Hillary Clinton was “treasonous” and “unpatriotic”.

Then on Thursday, as the White House struggled to contain the fallout from the book, a lawyer for the president sent a letter demanding Wolff and his publisher, Henry Holt & Co, “immediately cease and desist from any further publication, release or dissemination”, or excerpts and summaries of its contents. The legal notice, sent by the Beverly Hills-based attorney Charles Harder, also demanded a copy of the book.

Harder sent a similar letter to Bannon on Wednesday night, accusing the former chief strategist of violating an employee agreement and defaming the president.

The Guardian published details from the book on Wednesday after obtaining a copy from a bookseller in New England. New York magazine then rushed to publish a lengthy extract and more details began to emerge as major US publications including The New York Times and The Wall Street Journal received copies free from embargo.

About 250,000 copies of the book had already been shipped, supposedly to be held until Tuesday. On Thursday afternoon, a spokeswoman for Holt & Co said publication in all formats was being brought forward to Friday, “due to unprecedented demand”.

A statement from the publisher added: “Henry Holt confirms that we received a cease and desist letter from an attorney for President Trump. We see Fire and Fury as an extraordinary contribution to our national discourse, and are proceeding with the publication of the book.”

Wolff is due on NBC’s Today show on Friday morning for his first on-the-record interview.

Ben Wizner, director of the American Civil Liberties Union’s speech, privacy and technology project, said earlier Trump’s lawsuit had no chance of success.

“Even Donald’s Trump’s lawyers aren’t crazy enough to present this to a court,” he said. “It would be extraordinary and unprecedented for a court to respond to these claims by blocking publication. That is not going to happen.

“I think there is an audience of one for these legal threats and that’s Donald Trump.”

In a column for the Hollywood Reporter titled My Year Inside Trump’s Insane White House, Wolff gave more insight into what he discovered as he sat “day after day on a West Wing couch” for a year.

Administration officials, he suggested, do not believe Trump is capable of fulfilling his role as president.

“Everybody was painfully aware of the increasing pace of his repetitions,” Wolff wrote. “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.”

He added: “Hoping for the best, with their personal futures as well as the country’s future depending on it, my indelible impression of talking to them and observing them through much of the first year of his presidency, is that they all – 100 per cent – came to believe he was incapable of functioning in his job.”

In a final anecdote, Wolff wrote: “At Mar-a-Lago, just before the new year, a heavily made-up Trump failed to recognise a succession of old friends.”

Much of Thursday’s White House press briefing centred on the book. Sanders said any claims about Trump’s stability were “disgraceful and laughable”.

“If he was unfit, he probably wouldn’t be sitting there,” she said.

Trump appeared before the media earlier in the Roosevelt Room, where he was meeting Republican senators about immigration. There were shouted questions from reporters, including: “Did Steve Bannon betray you, Mr President? Any words about Steve Bannon?”

Trump replied: “I don’t know, he called me a great man last night, so, you know, he obviously changed his tune pretty quick.”

Wolff’s book – “filled with false and misleading accounts”, according to the White House – soared from 48,449th on Amazon’s bestselling books list to No 1.

The author said his book was based on more than 200 interviews, including multiple conversations with the president and senior staff. Sanders claimed Wolff “never actually sat down with the president” and had spoken with him just once, briefly, after Trump took office. She dismissed the book as “trashy tabloid fiction”.

“Aides thought they had more time to prepare for the book’s formal release,” The Washington Post reported. “Trump spent much of the day raging about the book to top aides, officials and advisers said … As he fumed, some aides were still frantically searching for a copy of the book.”

On Wednesday, Bannon hosted Breitbart News Tonight on Sirius XM radio as usual, making little reference to the public rupture.

When a caller brought up the issue, Bannon replied: “The president of the United States is a great man. You know I support him day in and day out.”