Impeachment may not help House Democrats, but I would bet it won’t hurt them in the way catastrophists fear. Swing-district Democrats can make a solid case this winter that Mr. Trump went too far, and then get back to talking prescription drug prices by the spring.

The Senate, though, is a different and more interesting matter. Right now, four Republican incumbents in swing (or swing-ish) states face competitive races: Martha McSally in Arizona, Cory Gardner in Colorado, Susan Collins in Maine and Thom Tillis in North Carolina.

Mr. Trump is underwater in all four states — narrowly in North Carolina, a bit less so in Arizona, and badly in the other two. But of course, among Republicans in those states, the president is presumably as popular as he is among Republicans everywhere.

Hence the quartet’s dilemma, if they are forced to consider voting whether to acquit Mr. Trump or convict him. Logic tells us that politically, they’ll want to vote to convict, with the probable exception of Mr. Tillis. For a Republican in a state where Mr. Trump isn’t popular, convict is a much safer vote than acquit.

However, the Republican parties in all these states are pretty Trumpy these days. In Maine, for example, the state party last January re-elected as its party leader a woman, Demi Kouzounas, who said her party had been “too nice.” This was during the tenure of a former governor, Paul LePage, known for saying nice things like “guys with the name D-Money, Smoothie, and Shifty” come to his state and impregnate white girls. Recently, the chairwoman said of impeachment: “Another day, another witch hunt in Washington, D.C.”

In other words, Ms. Collins — and the other three — could very well lose support in their own party if they vote to convict Mr. Trump. They are going to have a very tough year. (Senator Doug Jones, Democrat of Alabama, will face a similar Hobson’s choice, it should be noted.)

How tough a year will depend to some extent on how the majority leader, Mitch McConnell, decides to play things should the House send articles of impeachment to the Senate. Much speculation has swirled around whether Mr. McConnell would hold a trial at all. A tape emerged last week of him saying back in March that a trial would be required; others still suspect that the man who let Merrick Garland twist in the wind for all those months is capable of anything.