Since the election, numerous congressional Republicans have refused to publicly weigh in on any Trump proposal at odds with Republican orthodoxy, from his border wall to his massive infrastructure package. The most common reason, stated repeatedly but always privately: They’re afraid of being attacked by Breitbart or other big-name Trump supporters.

“Nobody wants to go first,” said Rep. Mark Sanford (R-S.C.), who received nasty phone calls, letters and tweets after he penned an August op-ed in The New York Times, calling on Trump to release his tax returns. “People are naturally reticent to be the first out of the block for fear of Sean Hannity, for fear of Breitbart, for fear of local folks.”

An editor at Breitbart, formerly run by senior Trump adviser Steve Bannon, said that fear is well-founded.

“If any politician in either party veers from what the voters clearly voted for in a landslide election … we stand at the ready to call them out on it and hold them accountable,” the person said. (Trump won the Electoral College handily but lost the popular vote by 2 percentage points.)

Republican Hill staffers have wrestled in recent months with how to respond to inquiries from Breitbart or other pro-Trump bloggers. Engage them or ignore them? One GOP aide told POLITICO members are “damned if you do, damned if you don’t.” Another said it’s having a “chilling effect” on GOP lawmakers.