The vast majority of congressional Republican lawmakers fall somewhere in between Ms. Murkowski and Ms. Greene — uneasy about bowing to Mr. Trump in perpetuity but equally unwilling to cross the party’s grass roots by partaking in any effort to drive him from the G.O.P.

As has been the case since the president’s election in 2016, the answer for dozens of G.O.P. members of Congress is to vote with their feet and retire. This week, Senator Rob Portman of Ohio announced he would do just that in 2022, sending many Republicans into a deeper state of dismay.

“I’ve been in Republican politics for 40 years professionally — so, just after Watergate — and I will tell you this has been the worst period of the entire time,” said Representative Tom Cole of Oklahoma, a longtime friend of Mr. Portman’s.