The legal notice — addressed to author Michael Wolff and the president of the book's publisher — said Trump's lawyers were pursuing possible charges including libel in connection with the forthcoming book, "Fire and Fury: Inside the Trump White House."
The letter by Beverly Hills-based attorney Charles J. Harder demanded the publisher, Henry Holt and Co., "immediately cease and desist from any further publication, release or dissemination of the book" or excerpts and summaries of its contents. The lawyers also seek a full copy of the book as part of their investigation.
The latest twist in the showdown came after lawyers accused Bannon of breaching a confidentiality agreement and Trump denounced his former aide as a self-aggrandizing political charlatan who has "lost his mind."
It marked an abrupt and furious rupture with the onetime confidant that could have lasting political impact on the November midterms and beyond.
The White House's sharp public break with Bannon, which came in response to unflattering comments he made about Trump and his family in a new book about his presidency, left the self-fashioned populist alienated from his chief patron and even more isolated in his attempts to remake the Republican Party by backing insurgent candidates.
Late Wednesday, lawyers for Trump sent a cease-and-desist letter to Bannon, arguing he violated the employment agreement he signed with the Trump Organization in numerous ways and also may have defamed the president. They ordered that he stop communicating either confidential and or disparaging information, and preserve all records in preparation for "imminent" legal action.
"You have breached the Agreement by, among other things, communicating with author Michael Wolff about Mr. Trump, his family members, and the Company, disclosing Confidential Information to Mr. Wolff, and making disparaging statements and in some cases outright defamatory statements to Mr. Wolff about Mr. Trump, his family members, and the Company," read the letter from lawyer Charles Harder.
In a lengthy statement issued in the afternoon, Trump blamed Bannon — his former campaign manager and chief strategist who now heads the conservative Breitbart News website — for everything from leaks to the news media to the upset GOP loss in last month's Senate race in Alabama. The president cast Bannon as a disgruntled former staffer whose chief goal is to stir up trouble.
"Steve Bannon has nothing to do with me or my Presidency," the statement said. "When he was fired, he not only lost his job, he lost his mind."
The White House also released a statement from the first lady's office condemning Wolff's book as a title to be found in the "bargain fiction" bin, while the Republican National Committee said Wolff has "a long history of making stuff up." White House press secretary Sarah Huckabee Sanders, meanwhile, devoted much of her Wednesday news briefing Wednesday to disputing Wolff's claims and seeking to undermine Bannon's credibility.
The response was a marked departure from mid-October, when Trump called Bannon "a friend of mine" and said he understood his perspective.
But the much anticipated account of life in Trump's White House caught the president and his West Wing team off-guard, with the president huddling with White House communications director Hope Hicks, one of his most trusted advisers, and Sanders to craft the fiery statement, after calling friends for much of the morning. Aides thought they had more time to prepare for the book's formal release.
Trump spent much of the day raging about the book to top aides, officials and advisers said, and Sanders described the president as "furious" and "disgusted." As he fumed, some aides were still frantically searching for a copy of the book, and even senior aides such as Hicks had not seen it by the afternoon, officials said.
"He's out of control," one person with knowledge of Trump's comments said. This person added that the president had been in an upbeat mood for much of Tuesday, continuing to brag about last month's passage of the Republican tax bill even as he fired off combative tweets.
Trump also blasted others in the White House for talking to Wolff, who was frequently spotted wandering the West Wing with no escort or ensconced in Bannon's office, especially during the early months of the administration.
Wolff said Trump was aware of the project and allowed others to participate. An excerpt of the book, published online in New York magazine, said the author conducted more than 200 interviews "over a period of 18 months with the president, most members of his senior staff, and many people to whom they in turn spoke."
Sanders said that Wolff "never actually sat down with the president" since Trump took office and that the two men had only had one five- to seven-minute conversation "that had nothing to do, originally, with the book."
One senior White House official said Trump advisers considered Wolff friendly and believed it would be beneficial to speak with him; this person also said that Wolff interviewed Trump. A second senior White House official said the president had viewed Bannon as a useful ally when he was frustrated with congressional leadership and that, while he didn't consider Bannon a close confidant, he also didn't want him as an enemy.
Allies said Bannon was largely incommunicado on Wednesday. He had considered issuing a statement denouncing the book and denying some of the quotes but was not able to do so before Trump went on the attack, they said.
After being forced from the White House in August, Bannon and the president still occasionally talked on the phone. But West Wing aides have long maintained that Bannon overstated the frequency of his calls with — and influence over — the president.
"If all of us are being honest with ourselves, I don't think you would have found more than 2 percent of politicians or reporters who knew who Stephen K. Bannon was," Rep. Peter T. King (R-N.Y.), said in a recent interview. "Trump had already won the nomination and the primary. Whether you like the president or not, he is responsible for his win."
A White House official said call logs show Trump has spoken with Bannon only five times since the former adviser left and the official said most of the calls were initiated by Bannon. Trump, however, often uses cellphones to talk with outside advisers and confidants.
Trump had complained for several months about portrayals of Bannon as a political "Svengali," according to one adviser who speaks with Trump frequently. "This has been a long time coming," the person said. Several others said the relationship may be irreparable.
"Steve doesn't represent my base — he's only in it for himself," Trump said in his Wednesday statement.
"Steve pretends to be at war with the media, which he calls the opposition party, yet he spent his time at the White House leaking false information to the media to make himself seem far more important than he was," the statement continued. "It is the only thing he does well. Steve was rarely in a one-on-one meeting with me and only pretends to have had influence to fool a few people with no access and no clue, whom he helped write phony books."
It remains unclear, however, whether Trump will exile Bannon indefinitely; the president often likes to cast characters out and then bring them back in and frequently maintains contact with those he has fired.
Wolff's book paints Trump as a buffoon who doesn't read, can't settle on political priorities and is unable to manage a warring cast of advisers who spend their days squabbling and undermining each other and the president.
In one scene, Katie Walsh, formerly a deputy chief of staff, is quoted as saying that dealing with Trump is "like trying to figure out what a child wants"; Walsh disputed that account Wednesday to an Axios reporter.
In another book scene, Sam Nunberg, a former campaign aide who was ultimately fired, describes trying to explain the Constitution to the president. "I got as far as the Fourth Amendment," the book quotes Nunberg as saying, "before his finger is pulling down on his lip and his eyes are rolling back in his head."
But, at least in the excerpts that have emerged so far, Bannon emerges as the most scathing critic of Trump and his family. Wolff portrays him as a master puppeteer, manipulating the president for his own political purposes.
Bannon is quoted describing a Trump Tower meeting during the campaign between Donald Trump Jr.; Jared Kushner, the president's son-in-law; and a Russian lawyer as "treasonous" and "unpatriotic." At another point in the book, he is quoted calling the president's daughter Ivanka Trump "dumb as a brick."
Wolff also depicts Bannon as harboring his own 2020 presidential ambitions.
The president and his team were already infuriated two weeks ago by a profile in Vanity Fair in which Bannon attacked a number of senior Trump advisers and seemed to mock the president. Trump had wanted to attack Bannon then, people familiar with the strategy said.
For months, Trump confidants — including aides such as Hicks and Kushner, lawyer Ty Cobb, and friends like Newsmax chairman Chris Ruddy and New Jersey Gov. Chris Christie (R) — have tried to persuade the president to cut ties with Bannon, who in recent months has backed insurgent Republicans such as failed Senate candidate Roy Moore in Alabama.
Bannon has in recent weeks also alienated his main financial backer, Rebekah Mercer, after he told several other major conservative donors that he would be able to count on the Mercers' financial support should he run for president, a person familiar with the conversations said. The person said Mercer now does not plan to financially support Bannon's future projects — and that she was frustrated by his moves in Alabama and some of his comments in the news media that seemed to stoke unnecessary fights.
A person close to Bannon said he was not running for president. Bannon and Mercer declined to comment through representatives.
"The core constituency for Breitbart is what you would call the Trump Deplorables. That's the audience. And if they're asked to choose between Steve and Trump, they're going to choose Trump. That's clear," said a person familiar with the company's ownership.
The West Wing response cheered many Trump advisers and congressional Republicans opposed to Bannon. At least two candidates supported by Bannon — including Senate hopeful Kelli Ward of Arizona — sought to distance themselves on Wednesday.
In a conversation with Trump on Wednesday, Senate Majority Leader Mitch McConnell (R-Ky.) praised the White House reaction.
"He told the president it was perfect and he wouldn't change a word," one person familiar with the discussion said.
Brian Murphy, Erica Werner, Rosalind S. Helderman, Carol D. Leonnig and John Wagner contributed to this report.