WASHINGTON — President Trump unleashed on his former chief strategist and campaign manager Wednesday, issuing a long and unusual statement questioning Steve Bannon’s mental stability, honesty, and political influence.

‘‘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. Steve was a staffer who worked for me after I had already won the nomination by defeating seventeen candidates, often described as the most talented field ever assembled in the Republican party.’’

Trump continued: ‘‘Now that he is on his own, Steve is learning that winning isn’t as easy as I make it look. Steve had very little to do with our historic victory, which was delivered by the forgotten men and women of this country. Yet Steve had everything to do with the loss of a Senate seat in Alabama held for more than thirty years by Republicans. Steve doesn’t represent my base — he’s only in it for himself.’’

The statement from Trump came after Bannon criticized Trump and his family in recent interviews — mocking the president’s intellect, criticizing the operations of the White House, and torching Donald Trump Jr. and the president’s son-in-law and senior adviser, Jared Kushner. His most recent comments, published online Wednesday in excerpts from a book by journalist Michael Wolff, came two weeks after a Bannon profile in Vanity Fair that infuriated the president and his senior aides.

In on-the-record interviews with Wolff, Bannon called a meeting between the Trump campaign’s top advisers and Russian representatives in mid-2016 ‘‘treasonous’’ and ‘‘unpatriotic’’ — furthering the narrative of Trump’s harshest critics.

Bannon also warned that special counsel Robert Mueller’s investigation into alleged Russian collusion will focus on money-laundering and the Trump family’s dealings with Deutsche Bank. Bannon, according to Wolff, predicted: ‘‘They’re going to crack Don Jr. like an egg on national TV. . . . They’re sitting on a beach trying to stop a Category Five.’’

The book, ‘‘Fire and Fury: Inside the Trump White House,’’ which paints an unflattering portrait of Trump’s campaign and administration, came after Wolff spent months in the White House — often in Bannon’s office. Trump was aware of the project and gave the blessing for others to talk to Wolff, the author said.

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 Trump was interviewed by Wolff.

The book essentially paints Trump as an unwitting 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 fighting.

Katie Walsh, formerly a deputy chief of staff, is quoted in the book as saying that dealing with Trump was like dealing with the whims of a child and that the White House could not decide on three main priorities six weeks into the administration.

Trump’s statement is likely to hearten congressional Republicans and advisers to Trump who have wanted him to distance himself from Bannon, who was forced out of the White House last summer and has returned to his perch as head of the conservative Breitbart News website.

But it remains unclear whether Trump will kick Bannon out forever; he often likes to cast characters out and then bring them back in, frequently maintaining contact with those he has fired.

For months, Trump confidants — from aides such as Kushner, Trump lawyer Ty Cobb, and communications director Hope Hicks to friends such as Chris Ruddy and Chris Christie — have tried to persuade him to cut ties with Bannon, who in recent months has worked to back insurgent Republicans such as failed Senate candidate Roy Moore of Alabama.

Trump was infuriated at Bannon’s latest remarks, telling senior aides and advisers that Bannon was ‘‘not well,’’ according to one person familiar with the president’s frustrations. He complained that Bannon again was trying to take credit for Trump’s election win. He huddled with Hicks and press secretary Sarah Sanders to craft Wednesday’s fiery statement after calling friends for much of the morning.

Trump aides also called people close to Bannon Wednesday and told them the White House was displeased with the former chief strategist, according to people familiar with the conversation.

Advisers have also tried to tell Trump that Bannon was not responsible for his win, that Bannon leaks damaging information to the news media, that he says things about the president that are not true, and that Bannon is more interested in Bannon than Trump. He has few close allies in the White House.

Trump and his senior team were already incensed with the recent Vanity Fair article in which Bannon attacked a number of senior Trump advisers and seemed to mock the president. Trump wanted his White House to attack Bannon after the story, people familiar with the president’s thinking said.

Then came Wolff’s book, in which Bannon is quoted hurling sharp criticism at members of Trump’s inner circle and family — including a fiercely critical account of the meeting between Trump’s son and a Russian lawyer.

The book quotes Bannon as saying: “The three senior guys in the campaign thought it was a good idea to meet with a foreign government inside Trump Tower in the conference room on the twenty-fifth floor — with no lawyers. They didn’t have any lawyers. Even if you thought that this was not treasonous, or unpatriotic . . . and I happen to think it’s all of that, you should have called the FBI immediately.’’

Advisers had told reporters for weeks that Bannon was instrumental in the book and that it was going to look ‘‘absolutely terrible’’ for the White House,’’ according to one senior official.

‘‘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,’’ Trump’s statement said.

‘‘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.’’

Material from the Associated Press was included in this report.