Odds are that after this year’s midterms, of the 17 Republicans in the House and Senate who voted to impeach or convict President Trump for trying to hold power after losing the 2020 election, only one, Alaska Sen. Lisa Murkowski, will still be in office. And if Alaska didn’t have a nonpartisan primary, she very well might not have made it out of her 2022 reelection bid.

Of the others who are still hanging on, Sen. Susan Collins (R-Maine) and Rep. David Valadao (R-Calif.) are favored in their primaries but face difficult general elections. Both have defied the odds before, but California’s gerrymandering counterstrike makes Valadao even more vulnerable. Meanwhile, the president’s effort to make Maine the next Minnesota makes life harder for Collins than in her surprise win in 2020 — which was before she voted to remove Trump from office.

That leaves Sen. Bill Cassidy (La.), who Decision Desk HQ’s Geoffrey Skelley convincingly argues is probably cooked like a cajun crawfish now that the GOP establishment has lined up behind his Trump-endorsed challenger, Rep. Julia Letlow, in the state’s now-closed primary.

Nothing speaks as powerfully of the president’s control of his party as the success of the impeachment purge. Like trophy heads mounted on the wall, the defeats or self-deportations of the “stop the steal” refuseniks serves as a constant reminder to incumbents. But it’s an expensive display.

Diversity helps parties prevent wipeouts in difficult cycles, like this one is for Republicans, and maximizes gains in good years, as astute Democrats are hoping to do this year. Coalitional parties do make governing harder, but the same factions that frustrate also guard against delusional thinking that leads to devastating losses.

Now, after going along with Trump for a wild ride of a year, Republicans find themselves in a similar situation. The killings of two protesters by federal immigration authorities in Minnesota bookended a bizarre episode in which the president managed to convince friends and foes alike that he might take Greenland by force.

Less than a month into the year, Republicans are surely missing the presence of the purged members. Their presence as harder opponents of the president made mainstream checks on Trump appear both milder and more pragmatic. Imagine how many times Senate Majority Leader John Thune (S.D.) has been able to tell the president, “It’s not me. It’s those pesky moderates.” The Susan Collinses of the Senate allow mainstream Republicans to curb Trump without having to fight him directly.