WASHINGTON — Stephen Bannon stepped down as executive chairman of Breitbart News Network on Tuesday, ending his relationship with the far-right website that he helped become widely influential and which in turn abetted his rise as a political adviser and would-be kingmaker.
Bannon’s departure — just days after his public criticisms of former White House colleagues led to a spectacular falling-out with President Trump and his allies — was a humbling denouement for a figure who had reached the uppermost levels of power only a year ago. It leaves him with no evident platform to promote his views and no financial basis for his preferred candidates.
Bannon left Breitbart in August 2016 to join Donald Trump’s presidential campaign and later served as President Trump’s chief White House strategist. He was fired by Trump almost exactly a year after formally signing up with him.
Bannon maintained his visibility by rejoining Breitbart in August and directing it to serve his political ends as the insurgent voice of the ‘‘anti-establishment’’ wing of the Republican Party, a faction that many critics saw as a socially intolerant and racist fringe of white nationalism.
His departure from Breitbart followed what appears to have been a vote of no confidence from a key supporter and investor in the website, Rebekah Mercer, a wealthy political donor, people at the company said. Mercer and her father, hedge-fund billionaire Robert Mercer, own a minority share of Breitbart and are influential voices in its operation.
Bannon provoked Rebekah Mercer’s ire by making critical comments about Trump and his family to author Michael Wolff for his book ‘‘Fire and Fury,’’ published last week. Bannon is quoted as saying that Trump’s son, Donald Trump Jr., and son-in-law, Jared Kushner, engaged in ‘‘treasonous’’ behavior by secretly meeting with Russian representatives during the campaign to get unflattering information about Trump’s opponent, Hillary Clinton.
Trump replied to Bannon’s comments with a statement savaging his former confidant. ‘‘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,’’ the president said. He later attacked Wolff and the book in a tweet in which he referred to Bannon as ‘‘Sloppy Steve.’’
Mercer weighed in with a rare statement of her own on Thursday that distanced her from Bannon. ‘‘I support President Trump and the platform upon which he was elected,’’ she wrote, adding that her family had ‘‘not communicated with Steve Bannon in many months and have provided no financial support to his political agenda, nor do we support his recent actions and statements.’’
Although Bannon continued to chair Breitbart’s editorial meetings and host its satellite-radio program, Mercer’s comments appeared to signal his end, people at the media company said. Breitbart’s readers seemed to side with Trump in the spat.
As late as this weekend, Bannon continued to tell people that he planned to stay in charge at Breitbart and that he would keep his radio show. He argued that the show and the site were doing better than ever, even though associates have questioned whether that was true.
The former chief strategist continued to tell others that Trump would forgive him, and the president was only a ‘‘vessel’’ in the movement and that the president was transactional. He continued to say that Breitbart chief executive Larry Solov supported him and what he was doing with the site while downplaying Rebekah and Robert Mercer’s public split with him.
Some conservatives who have worked closely with Bannon were harsh in response, all but writing his political obituary in the hours after the announcement.
‘‘He’s gone from the top of the mountain to the deepest valley, and it was all self-inflicted,’’ said veteran GOP strategist Edward Rollins, who has worked with Bannon and is chairman of Great America, a pro-Trump group. ‘‘Breitbart was his voice and it’s been taken away from him, leaving him with nothing.’’
In a statement carried on Breitbart’s website, Bannon said, ‘‘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.’’
The Mercers were largely responsible for Bannon’s place at Breitbart, and vice versa; Bannon introduced them to the site’s founder, Andrew Breitbart, in 2011, and helped persuade them to invest $10 million in Breitbart’s vision of an insurgent conservative media outlet that would take on Hollywood, the news media, and established Washington figures, including conventional Republicans.
In exchange for their investment, the Mercers secured a seat for Bannon on Breitbart’s board. When Breitbart died of a heart condition months later, Bannon took over the operation.
He then set about turning it into a clarion of economic populism and nationalist sentiment. It advocated for strict limits on immigration, particularly from Latin America and from Muslim-majority nations, and for an ‘‘America first’’ agenda in trade negotiations. Its political philosophy was amplified by Trump when he announced his candidacy in 2015, although Breitbart steered a relatively even line during the early primaries between Trump and Republican challenger Ted Cruz, the Mercers’ preferred candidate.
Bannon at one point described Breitbart as ‘‘the platform for the alt-right,’’ a phrase that became associated with white separatism, anti-Semitism, and generally racist sentiments. Breitbart’s editors insisted the site endorsed none of those views.
Nevertheless, Breitbart soared under Bannon, reaching 37 million unique readers a month before Trump upset Hillary Clinton to win the 2016 election. Among the writers he championed was Milo Yiannopoulos, who elicited both a rapturous response from Breitbart’s readers but heavy criticism elsewhere for columns about lesbians, blacks, and Muslims.