Steve Bannon’s midterm insurgency to upend the Republican establishment in Congress appeared dead Thursday after a nasty break with President Trump cost him credibility and institutional support.

Republican donors pulled crucial financial backing and challengers in targeted primaries distanced themselves, as so-called establishment candidates turned the tables on Bannon by reaffirming their alliance with Trump and demanding their opponents excommunicate the president’s former top adviser.

“A Bannon insurgency is poof,” said a conservative operative who supports anti-establishment primary challengers, and requested anonymity in order to speak candidly. “I’m thinking of calling a couple of candidates who I took in to meet with Bannon and saying: ‘If you feel the need to distance yourself from Bannon and align with Trump, do it.’”

Bannon, executive chairman of Breitbart News, was ascendant in GOP circles because of his association with Trump. He served as CEO of the president’s 2016 campaign during its final three months and transitioned to the job of White House chief strategist, until he departed in August.

Bannon remained a close confidant of Trump, talking to the president often.

His stature elevated after the conservative challenger he backed in a late September special Senate election primary in Alabama defeated Senate Majority Leader Mitch McConnell’s pick. Suddenly, Republican donors and party establishment figures courted Bannon, wanting to associate themselves with his planned 2018 insurgency against incumbents.

Overnight, Bannon became a pariah as revelations of his comments critical of Trump and his family, revealed in an upcoming book, spread.

“Bannon’s primary objective should be helping Trump to enact his agenda,” said Dan Eberhart, a wealthy Republican donor in Arizona who was working with the nationalist firebrand to build support for insurgent Senate primary challengers.

“I believe he presumes there is a massive grassroots army behind him. I think the reality is more muted,” Eberhart added. “I am not sure that all this helps him support Bannonite candidates down the road.”

A second Republican donor and bundler who met with Bannon in recent months, speaking on condition of anonymity, expressed relief that he didn’t get involved with the insurgent and is unlikely to be publicly identified with him.

Bannon’s loss of financing, more than being shunned again by a Republican apparatus that had embraced him because of his ties to Trump, is the biggest blow to his insurgency. It was already questionable after his candidate, retired judge Roy Moore, lost a high-profile special election last month to now-Sen. Doug Jones, D-Ala.

This week’s ugly divorce with Trump sealed his exile.

A Republican source confirmed to the Washington Examiner on Thursday that Bob Mercer and his daughter Rebekah Mercer, expected to funnel millions into campaigns and super PACs for Bannon-backed challengers, were cutting all ties, such that his future at Breitbart News could be tenuous.

Without the Mercers, other deep-pocked conservative donors that might have stepped forward to underwrite Bannon are sure to stay away.

“What mattered was the Mercers were going to write a $25 million check to fund these activities and that’s not happening,” said the conservative operative who works with anti-establishment challengers.

A spokesman for Bannon did not respond to a request for comment. On Breitbart's radio show, Bannon said he admires Trump and will stay focused on helping the president enact his agenda.

Candidates on both sides of the divide responded swiftly. So-called establishment favorites sought the political advantage with calls for their populist challengers to condemn Bannon, who in turn tried to mitigate the damage of their association with him.

In West Virginia, Rep. Evan Jenkins and state Attorney General Patrick Morrisey are competing in an open GOP primary to challenge Democratic Sen. Joe Manchin. Jenkins, dubbed McConnell’s preferred candidate in stories published by Breitbart News, seized the offensive.

On Wednesday, he issued a statement demanding that Morrisey drop Bannon, who had previously endorsed him in a move seen as damaging to Jenkins. Morrisey obliged, with his campaign spokesman telling CNN that the candidate “does not support these attacks on President Trump and his family.”

Bannon-backed challengers in Mississippi and Nevada were the exception, as Chris McDaniel, eyeing a race against Sen. Roger Wicker, R-Miss., and Danny Tarkanian, running against Sen. Dean Heller, R-Nev., declined to criticize their political patron, according to BuzzFeed News.

Heller, whose occasionally rocky relationship with Trump could be problematic in the primary, used Bannon’s feud with the president to solidify his ties to the White House.

"Danny Tarkanian and Steve Bannon are frauds whose only skill is losing elections and costing Republicans seats," Heller spokesman Keith Schipper said.