WASHINGTON (Reuters) - Steve Bannon has stepped down as executive chairman of Breitbart News, the right-wing news website said on Tuesday, after the former White House chief strategist drew fire from President Donald Trump for harshly criticizing his eldest son.

Bannon was quoted in a new book about the Trump White House as calling Donald Trump Jr. “treasonous” and “unpatriotic” for meeting during the 2016 presidential campaign with a Russian lawyer who was said to have damaging information on Democratic candidate Hillary Clinton.

The comments drew a furious response from President Trump, who said Bannon “had lost his mind.”

Their public fight ended an alliance that began when Bannon joined the Trump campaign and helped the political novice defeat Democrat Hillary Clinton in the 2016 presidential election.

Bannon was fired by Trump in August as the president tried to bring order to feuding factions in the White House, but the two men continued to communicate and Bannon had remained an ally.

Losing his Breitbart post threatens Bannon’s dream of leading a new political movement that challenges the Republican establishment and supports his “America First” agenda of tougher trade deals and immigration laws.

Bannon has also lost his talk show on SiriusXM radio, the company said on Tuesday. Sirius said in a statement its programming agreement was with Breitbart, not with Bannon.

FILE PHOTO: Former White House Chief Strategist Steve Bannon speaks during a campaign event for Republican candidate for U.S. Senate Judge Roy Moore in Fairhope, Alabama, U.S., December 5, 2017. REUTERS/Jonathan Bachman/File Photo

In an effort to try to repair the damage from the book, Bannon said his “treasonous” comment was directed at a former Trump campaign manager, Paul Manafort, who also attended the meeting at Trump Tower. The author of the book, Michael Wolff, disputed Bannon’s account.

“Bannon died of his own sword,” said Roger Stone, a long-time Trump friend. “A classic example of hubris and beginning to think you are smarter than the boss.”

Wolff’s book, “Fire and Fury: Inside the Trump White House,” characterized Trump as mentally unstable, inept and unprepared for the presidency.

After publication of the book last week, major Republican Party donor Rebekah Mercer, who owns a stake in Breitbart, issued a statement distancing herself from Bannon, saying she did not support his “recent actions and statements.”

SUPPORTED ROY MOORE

Bannon joined Breitbart in 2012 and helped raise the profile of the news site, which he once called the platform for the so-called alt-right, a loose confederation of neo-Nazis, white supremacists and anti-Semites.

“I’m proud of what the Breitbart team has accomplished in so short a period of time in building out a world-class news platform,” Bannon said in a statement cited by Breitbart News.

Bannon did not immediately respond to a request for comment from Reuters.

Breitbart Chief Executive Larry Solov, in a statement on the organization’s website, called Bannon “a valued part of our legacy.”

“We will always be grateful for his contributions, and what he has helped us to accomplish,” Solov said.

After leaving the White House in August, Bannon picked a fight with the Republican establishment that may have cost the party a U.S. Senate seat in deeply conservative Alabama.

He supported Republican Senate candidate Roy Moore in his primary fight against incumbent Luther Strange, who was backed by Trump and mainstream Republicans.

Moore won the primary but lost to Democrat Doug Jones in December’s general election after Moore was accused of sexual misconduct against teenagers.