But the most acute danger for the health of the party, and its electoral prospects to retake the House and Senate in 2022, is the growing chasm between the pro-Trump voter base and the many Republican leaders and strategists who want to reorient for a post-Trump era.

“Have you heard what some of these folks waving MAGA flags are saying about Republicans?” said Representative Peter Meijer, Republican of Michigan, whose first days in Congress this month were marked by evacuations to escape from a mob. “They don’t identify themselves as Republicans.”

Mr. Meijer was among the Republicans who voted to affirm President-elect Joseph R. Biden Jr.’s Electoral College victory last week, in the proceedings that rioters incited by Mr. Trump interrupted. The vote set off another round of vitriol and threats.

“Our expectation is that somebody will try to kill us,” said Mr. Meijer, an Iraq war veteran. “That is the scenario that many of us are preparing for.”