Tensions between President Trump and Steve Bannon, his former chief strategist, exploded into open warfare on Wednesday with the publication of excerpts from a forthcoming book about the presidency.

After reading on Wednesday in excerpts of the book that Bannon had accused Trump's son of conducting a "treasonous" meeting with Russians, Trump said Bannon had "lost his mind" in a scathing official statement that claimed the Breitbart News chief had "spent his time at the White House leaking false information to the media to make himself seem far more important than he was."

Bannon's allies said the public feud between him and Trump was not surprising given the dynamics of their rocky relationship.

"This was ultimately inevitable," a source close to Bannon told the Washington Examiner. "It's two very strong personalities and we all knew it was going to happen."

That source said he would advise Bannon against matching the president's vitriol, however.

"I'm going to tell him to stay calm and not say anything. I think it's in Steve's best interest to just take it," the source said. "Everybody [in Bannon's circle] was like, no one speak to the press."

"I think Steve's comments gave the implication that the Trump Organization engages in criminal activities, which it absolutely doesn't," the source added of Bannon's comments as reported in excerpts of the book, "Fire and Fury: Inside the Trump White House," that were published Wednesday. "Between that and attacking the president's family, it's frankly a no-no."

Trump's statement about Bannon having "lost his mind" burst into public view a conflict between the two men that had simmered since before Bannon left the West Wing. And in the months since Bannon's departure, the Breitbart News chief has made life difficult for the White House in which he once served.

During the Alabama GOP Senate primary, for example, Bannon backed Republican candidate Roy Moore in the GOP primary while Trump backed former GOP Sen. Luther Strange, who ultimately lost. Bannon encouraged Trump and his allies to back Moore in the general election, only to have Moore's candidacy implode amid a sexual misconduct scandal that handed the Alabama Senate seat to a Democrat for the first time in decades.

At the height of stories about Bannon's internal clout last year, Trump sought to quiet the speculation by telling the New York Post in April that his chief strategist was simply "a guy who works for me."

The president was said to be irritated about Bannon's cooperation with the author of a book, "Devil's Bargain" by Joshua Green, that depicted Bannon as the custodian of the Trump zeitgeist. The book was published in July, while Bannon still worked in the West Wing.

Some presidential allies viewed Bannon as the potential source of leaks about the White House's internal power dynamics. Others saw Trump's chief strategist as a primarily self-serving climber who traded on the president's success even before his departure from the administration.

One of Bannon's top critics briefly worked alongside him in the West Wing. Former White House communications director Anthony Scaramucci, who precipitated his own removal in July by delivering a profanity-laced tirade to a reporter that included a screed against Bannon, took a victory lap on Wednesday as the president lashed out at his erstwhile colleague.

"I said what I said in the Summer," Scaramucci tweeted shortly after the White House began its pushback on the book. "[T]ake out the expletives and pay closer attention."

Reached by text message on Wednesday, a source close to Bannon laughed off the president's attacks on his former top aide. "Lol!!!" the Bannon ally said.

Another Bannon ally was even more defiant in the face of Trump's ire.

"The president is the one who has lost his fucking mind," the Bannon ally said.

Spokespeople for the White House and first lady hit back at the claims laid out in the book, which will be published in full on Jan. 9.

“This book is filled with false and misleading accounts from individuals who have no access or influence with the White House," press secretary Sarah Sanders said in a statement on Wednesday.

"The book is clearly going to be sold in the bargain fiction section," said Stephanie Grisham, spokeswoman for Melania Trump.

However, Michael Wolff, the author of the book, has said he conducted more than 200 interviews with everyone from Trump himself down to lower-level staffers, and said he wrote the book after taking up "something like a semi-permanent seat on a couch in the West Wing." Wolff has said Trump even encouraged the arrangement that allowed him to write such a comprehensive account of the president's first few months in office.

Bannon did not respond to a request for comment.