“The president was buoyed to election by capturing the hearts and minds of a populist, nationalist movement,” Alex Marlow, Breitbart’s editor in chief, said Friday evening. “A lot of it was anti-Wall Street, anti-corporatist, anti-establishment. And now we’re seeing that a lot of these guys remaining inside the White House are exactly the opposite of what we told you you were going to get.”
Mr. Bannon’s long enemies list will include anyone he deems hostile to the nationalist, conservative agenda that he viewed himself as the guardian of the White House. And his most personal causes will involve some the biggest fights that lie ahead between President Trump and Congress.
Most immediately, he has told associates that he wants to ensure that any spending resolution approved next month by Congress includes money to begin construction on the wall that Mr. Trump has promised to build on the southern border.
If Congress balks, Mr. Bannon has advised the president to issue a veto, which would trigger a government shutdown.
“You can’t play by the Marquess Queensberry’s rules,” he often tells colleagues, using a characteristically colorful historical analogy, in this case to the 19th-century code of conduct for boxing.
Whether he punches hard is not in doubt. The question that he and other like-minded conservatives see as fundamental for their cause is whether their efforts will have any effect on a White House that they fear is now dominated by people whose worldview is decidedly more moderate than Mr. Bannon’s.
Mr. Kushner; Ms. Trump; Dina Powell, the deputy national security adviser; and Mr. Cohn have all been the target of unrelenting attacks by Breitbart and others on the right for their efforts to draw Mr. Trump to the political center. The site has routinely dismissed Mr. Cohn as a “globalist” and a “swamp creature”; in headlines, his name would sometimes appear bracketed by globe emojis, to underscore the point — also an allusion to the triple parentheses that anti-Semites on social media use to denote Jewish names.
Breitbart has mocked Ms. Powell and Mr. Kushner for partying together in the Hamptons with members of the “fake news” media and Democratic politicians.
“We’re going to have a keen eye to see if Trump is able to continue connecting with his base, as the numbers just become more overwhelmingly globalist, centrist, establishment Democrat, all of those in the mix, and a lot less populist-nationalists,” Mr. Marlow said.
Now the scenario that many conservatives long feared is reality: The centrist aides are going to be largely unchecked.
“With Bannon gone, who is left to help the president shepherd his agenda through the establishment morass that wants to sink it?” said Laura Ingraham, the conservative radio host and author, who is among the most vocal proponents of the tighter immigration and trade policies the president campaigned on. “Conventional Wall Street Republicans didn’t elect Donald Trump, and they won’t save him. A laser beam focus on advancing his policies on trade, tax reform, immigration and infrastructure will.”
The veteran conservative activist Richard Viguerie questioned on Friday whether Mr. Bannon’s ouster was part of a looming “purge of conservatives on the White House staff.”
With Mr. Bannon no longer under any obligation to feign interest in working with Mr. Ryan and Mr. McConnell — whom he privately denigrated to Mr. Trump as backstabbers who would inevitably sell him out — the likelihood of a deepening and potentially paralyzing rift between the Republican Party’s hard-line conservatives and its leadership has only grown.
Congressional Republicans have never been very enthusiastic about the pieces of Mr. Trump’s agenda that most animated his core supporters. The president’s proposal to cut legal immigration by half over the next 10 years fell flat on Capitol Hill.
He is still waiting for approval of funding to build the border wall — perhaps the central promise of his campaign. And talks to move forward with a major infrastructure improvement package have stalled.
In one bit of parting advice to the president, Mr. Bannon urged Mr. Trump not to sign any government funding agreement that does not contain funding for the wall. But others in the White House have counseled the president not to pick that fight, which would lead to a government shutdown that could have disastrous political consequences. Republicans, in control of the White House and both chambers of Congress, would have no one to blame but themselves.
Breitbart is expected to be unsparing in its coverage of the issue. And Mr. Marlow said the absence of conservatives like Mr. Bannon was not a good sign.
“At Breitbart, our thoughts are that the president can certainly do a great job despite that, but we don’t think that is working for him all that well at the moment,” Mr. Marlow said.
Few who know Mr. Bannon believe he will waste much time before commencing the messy business of turning against the people he had spent the past seven months trying to work with.
“He will use Breitbart as a battering ram,” said Ben Shapiro, a conservative writer and commentator who used to work for Mr. Bannon when he was the executive chairman of the website, before he went to work for Mr. Trump. “Steve and subtlety have never shaken hands.”
In recent days, Mr. Bannon has been an isolated figure, keeping to his temporary office in the Eisenhower Executive Office Building next to the West Wing while the White House undergoes renovations. Mr. Bannon stayed behind in Washington while Mr. Trump and other senior aides traveled to the president’s golf club in Bedminster, N.J.
Unable to talk face-to-face with the president and sensing that his days were numbered, Mr. Bannon began to speak more openly with associates about how effective he could be if he returned to Breitbart and led a campaign-style assault against the Washington interests that he believed were preventing Mr. Trump from being the “America First” president he promised to be.
Representative Steve King of Iowa, a conservative Republican and antagonist to his party’s leadership, described Mr. Bannon as closest to the ideology that elected the president. And if Mr. Bannon is able to be a stronger advocate for that ideology outside the White House than he was within, all the better, Mr. King added.
“I want to see him effective in public life,” he said. “And I want to hear his voice, and I want it to have leverage.”