The question now: Does Mr. Bannon need Breitbart News more than Breitbart News needs Mr. Bannon?
“People who go to Breitbart don’t go there everyday because they give a damn about Steve Bannon,” said Kurt Bardella, a former Breitbart spokesman. “We could be looking at a new world order here in terms of who will occupy the space of Donald Trump’s preferred conservative platform.”
Mr. Bannon appears to be trying to stay at Breitbart. His penance began on Sunday, with a public statement in which he attempted to distance himself from his portrayal in Mr. Wolff’s book. For one thing, he claimed, his description of a 2016 meeting between Russians and Donald J. Trump Jr. as “treasonous” was intended to criticize Mr. Trump’s former campaign chairman, Paul Manafort, not the president’s son.
Media figures more famous than Mr. Bannon have learned the hard way that audiences tend to remain loyal to institutions, rather than individuals. For Mr. Bannon, the possibility of losing control of Breitbart — the vehicle that propelled him into the national spotlight, and eventually the highest echelons of power — could present a significant test to his potency as a leader of a political and cultural movement.
Among the most unsettling developments for the Bannon camp was losing the support of Ms. Mercer, a hard-line conservative donor, who said on Thursday that her family had ceased communicating with Mr. Bannon and denounced his statements in the Wolff book. “I have a minority interest in Breitbart News and I remain committed in my support for them,” Ms. Mercer said in a statement.
Perhaps luckily for Mr. Bannon, Ms. Mercer cannot unilaterally dismiss him from his company. Mr. Bannon’s fate was probably in the hands of Breitbart’s other owners — the family of Andrew Breitbart, the founder, who died in 2012, and its chief executive, Larry Solov, the former Breitbart News general counsel and childhood friend of its founder.
Representatives of Mr. Bannon and Breitbart News did not respond to inquiries over the weekend about Mr. Bannon’s future at the site.
Under Mr. Bannon, who assumed stewardship after Mr. Breitbart’s death, Breitbart News moved from a scorched-earth fringe site — known mostly for publishing incendiary articles that were deemed sexist, racist and xenophobic — to an unlikely voice for disaffected conservatives and a rallying place for passionate supporters of Mr. Trump.
Its readers remain faithful to the president, a fact that Mr. Bannon seemed to acknowledge in his statement on Sunday.
“I am the only person to date to conduct a global effort to preach the message of Trump and Trumpism, and I remain ready to stand in the breach for this president’s efforts to make America great again,” he wrote.
Mr. Bannon’s aggressive style and creative agitprop were clear factors in Breitbart’s recent success. On Facebook, its reach now rivals news organizations like Yahoo and The Washington Post. The site hired correspondents in Europe and the Middle East, and poached reporters from establishment news organizations like The Wall Street Journal.
In Washington, Mr. Bannon kept a residence at the so-called Breitbart Embassy, a Capitol Hill townhouse controlled by the site, where he courted candidates and threw V.I.P.-filled soirees. A recent book party for Laura Ingraham, the Fox News host, attracted prominent journalists and White House officials.
But as Mr. Bannon nurtured his real-world aspirations, Breitbart’s audience waned from the heights of last year’s presidential race. In November, the site received 13.7 million unique visitors in the United States, according to data from comScore, down about 20 percent from last January. It also lost advertisers who did not want their brands to appear alongside Breitbart articles.
The site struggled for acceptance in other ways, too. Despite employing a full-time reporter in the White House, Breitbart’s application for Congressional press credentials was denied. Its hunt for a larger headquarters in Washington was stymied by some commercial landlords who were uncomfortable about housing the business.
Mr. Bannon, a tenacious and shrewd operator, may yet cling to his Breitbart chairmanship, and Mr. Trump is known to re-embrace associates even after public defenestrations. The campaign manager whom he fired in 2016, Corey Lewandowski, remains a close adviser.
On Sunday afternoon, a blaring, all-capital-letters headline on Breitbart.com announced to readers that, reports notwithstanding, its leader was sticking with their cause. “Steve Bannon Issues Statement,” the headline read. “My Support Is ‘Unwavering’ for Trump and His Agenda.”