A vote to acquit, however, will force every senator to own Trump’s emboldened rhetoric of being exonerated. Which means they’ll have to defend Trump when the next embarrassing audio recording hits the airwaves, or when another witness surfaces to speak, or when John Bolton’s book comes out, or when internal memos about the “drug deal” come out via the Freedom of Information Act. Republican senators will become full-time exonerators.

That dilemma is now playing out in real time. Some 63 percent of voters in Arizona, Colorado, Maine and North Carolina look unfavorably on the Senate’s decision to date to disallow witnesses and hide documents — yet all five senators mentioned earlier have, so far, voted against transparency. That may partly explain why the five Republican senators are “underwater,” meaning that more constituents view them negatively than positively. And if that snapshot bodes poorly, the trend lines are worse: In the last quarter of 2019, McSally and Collins saw 5- and 4-point drops, respectively, in their “net” approval rating — an indication that a rising share of their constituents view them in a negative light.

For years, I’ve believed that the balance of the Senate almost invariably followed the outcome of a presidential election. This coming year, by contrast, the Trump impeachment may have such inertial power that the old truism of nationalized results during presidential cycles may no longer be valid. If so, the current trial, if you can call it that, will “decouple” the battles for the White House and the world’s “greatest deliberative body.”