Now, the man who took considerable credit for President Trump's shocking win in 2016 finds himself cast out - most importantly, from the good graces of Robert and Rebekah Mercer, the billionaire GOP donors who fund Breitbart and a variety of other Bannon-linked ventures. He's also losing his daily show on the conservative talk station on satellite radio network SiriusXM.
Bannon sought to make amends in a statement on Sunday, but a White House spokesperson said it didn't change his standing with the president.
Former White House chief strategist Stephen Bannon, in the book, described Donald Trump's son-in-law Jared Kushner's meeting with a Russian lawyer as "treasonous" and "unpatriotic".
"I support President Trump and the platform upon which he was elected", Mercer said in the statement, which was provided to The Washington Post. The author of the book, Michael Wolff, disputed Bannon's account. "A classic example of hubris and beginning to think you are smarter than the boss".
"The President has been very clear on his thoughts; issued a four-paragraph statement about Mr Bannon".
"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 carried on Breitbart's website.
Breitbart announced Tuesday that Bannon has stepped down as executive chairman of the conservative news site. Steve is a valued part of our legacy, and we will always be grateful for his contributions, and what he helped us to accomplish.
Moore won the primary but lost to Democrat Doug Jones in December's general election after Moore was accused of sexual misconduct against teenagers.