It leaves him with no evident platform to promote his views and no financial basis for his preferred candidates.
His reward was a key job inside the White House where, as chief strategist, he was seen as stoking the nationalist flame of Mr Trump's presidency.
Insiders says Bannon had two choices: Resign or be fired.
Bannon stepped down from Breitbart on Tuesday, capping a stunning rise and fall from the political fringe to the West Wing to whatever is fringe-ier than the fringe.
In an effort to try to fix the damage from the book Fire and Fury: Inside the Trump White House, Bannon said his "treasonous" comment was directed at a former Trump campaign manager, Paul Manafort, who also attended the meeting at Trump Tower. Bannon was harshest toward Don Jr., who came under fire a year ago for his campaign meeting with a Russian lawyer. After he left the administration, Bannon returned to his post leading the right-wing website Breitbart, where he continued to oversee positive coverage of Trump.
Bannon steps down from Breitbart News after break with Trump
Of course, Steve Bannon plays a large part in this account, and Wolff indicates that Bannon and other Trump staffers (including Trump's family) conflicted constantly.
Trump responded at the time by slamming him in a fiery statement, saying Bannon had "lost his mind". So when Bannon alienates Trump and Trump bucks, the decision isn't hard for the Mercers or for Breitbart to pick a side. One said Bannon was telling people as recently as Monday that he expected to stay on. He argued that the show and the site were doing better than ever, even though associates have questioned whether that was true.
Some conservatives who have worked closely with Bannon were harsh in response, all but writing his political obituary in the hours after the announcement.
Hansen said he won't know until he gets the royalty statement how many books he's sold since Friday. He took it to the Trump campaign, where Trump surely appreciated having a kindred spirit, and then to the White House.