President Donald Trump is blasting his former chief strategist ahead of the release of a new, unflattering book.

Trump says in the statement Wednesday that when Bannon was fired, "he not only lost his job, he lost his mind."

A new book by writer Michael Wolff offers a series of explosive revelations, including that Trump never expected to win the 2016 presidential race.

An adaptation of "Fire and Fury: Inside the Trump White House" published Wednesday in New York magazine says Trump believed his nomination would boost his brand and deliver "untold opportunities."

An excerpt published by The Guardian says Bannon described a Trump Tower meeting between the president's son and a group of Russians as "treasonous" and "unpatriotic."

In June 2016, Trump Jr., Paul Manafort and Jared Kushner met with Russian lawyer Natalia Veselnitskaya at Trump Tower in New York. Rob Goldstone, an associate of Trump Jr., had told Trump Jr. that the Russians had damaging information on Democratic presidential candidate Hillary Clinton. 

When Trump Jr. claimed that there was in fact nothing worthwhile on Hillary Clinton that came out of the meeting, according to the Guardian, Wolff writes that Bannon ridiculed Trump Jr., Manafort and Kushner. 

"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 25th floor – with no lawyers. They didn't have any lawyers," Bannon said. "Even if you thought that this was not treasonous, or unpatriotic, or bad s***, and I happen to think it's all of that, you should have called the FBI immediately."

Bannon went on to talk about what he thinks they should have done instead, which would have been to have the campaign's lawyers meet with the Russians and let the material be "dumped" to Breitbart or "maybe some other more legitimate publication." With that approach, "You never see it, you never know it, because you don't need to … But that's the brain trust that they had," Bannon added.

Special Counsel Robert Mueller, who was appointed in May to take over the Russia investigation after the president fired FBI Director James Comey, has indicted Manafort and his associate Rick Gates on money laundering charges, and former National Security Adviser Michael Flynn has pleaded guilty to lying to the FBI. 

Trump has consistently denied colluding with Russia. 

Wolff told the Guardian that he spoke to Trump and a number of senior officials and advisers for "Fire and Fury,"and he said that one recurring theme in the book is the "rancor" between Bannon and Kushner and Ivanka Trump, the president's daughter. He quotes former Secretary of State Henry Kissinger, who has advised Trump, as well as Kushner, as saying, "It is a war between the Jews and the non-Jews." Kushner and Ivanka Trump are both Jewish. 

Wolff also says in the book, according to the Guardian, that one of Trump's outside advisers and a close friend, billionaire Thomas Barrack Jr., said of the president, "He's not only crazy, he's stupid."

Trump attorney Ty Cobb declined comment.

Here is the president's statement in full: 

"Steve Bannon has nothing to do with me or my presidency. 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.

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. 

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. 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. 

We have many great Republican members of Congress and candidates who are very supportive of the Make America Great Again agenda. Like me, they love the United States of America and are helping to finally take our country back and build it up, rather than simply seeking to burn it all down."

(The Associated Press, CBS News contributed to this report.)