Washington — They wander the halls of public buildings and haunt receptions like the ghosts of the GOP past — the cohort of Republican senators and House members who will be leaving office with the arrival of the new Congress. Some chose retirement because they did not want to do what is necessary to keep office in Donald Trump’s party. Others were forcibly retired by the Democratic midterm wave.

The class of departing Republicans includes a few who won’t be missed. (Hint: One has a last name starting “Rohrabache-“.) But many of the House losses came in suburban districts that required outreach beyond the Trump-intoxicated base. Nationally, Democrats won about 70 percent of votes in suburban House districts. This means the grim political reaper came for some of the most reasonable elements of the party. This process is the reverse of natural selection — call it the survival of the witless.

Under typical circumstances, departing Republican officeholders would be obvious recruits for administration jobs. Is there any doubt that retiring Sen. Bob Corker, R-Tenn., would have been a prime candidate for secretary of state in a more normal GOP administration? Others would be natural fits for the lesser Cabinet jobs. But as Trump’s party purifies itself, true talent becomes a waste product.

In an incomplete, unrepresentative survey, conducted at think tank events and in buffet lines, departing members have told me a few things. They uniformly wonder why a president presiding over a 4 percent unemployment rate made immigration — actually, brown people invading the country who needed to be stopped by a deployment of the U.S. military — the substance of his midterm appeal. This strategy did nothing to answer the flood of Democratic attack ads on health care.

Departing GOP members also wonder why Trump nationalized a midterm election that could have been better fought on local issues and conditions. More than two-thirds of Americans cast their midterm votes to send a message about the president, either positive or negative — a recent record. It was once said of Teddy Roosevelt that he wanted to be “the bride at every wedding.” Trump seems compelled to be bride, groom, minister, wedding singer and drunken guy giving the off-color champagne toast.

And departing members report that the most active Republican partisans in their state believe that there is nothing — absolutely nothing — wrong with a political party that lost 40 House seats in a time of relative peace and unprecedented prosperity. If anything, one soon-to-be-former member told me, the Republican base believes its party lost ground because it wasn’t true enough to Trump’s agenda. In this parallel political reality, building the border wall would have stopped the Democratic wave.

So where does this leave American politics headed into the 2020 presidential election? Trump’s party — predominantly based in rural, small-town and smaller city America, and disproportionately older, male, less educated and white — is genuinely enthusiastic about its disruptive leader. Urban and (increasingly) suburban Americans — disproportionately younger, female, more educated and multicultural — are finally getting the picture that they are Trumpism’s foils. And measured by Democratic donations and turnout, they aren’t happy about it.

This leaves a few of us entirely homeless in American politics. If you had asked me 10 years ago, when I left government, if the Republican Party could be won and rallied with George Wallace’s campaign themes, I would have thought you ridiculous. Now it is my naivete that deserves ridicule. If a significant portion of the GOP finds this equally disorienting, it is being disoriented in silence.

Trump is a politician famous for following his “gut” to some odd and sketchy places. But the political question of the 2020 presidential election is quite practical: Can Trump keep Michigan, Wisconsin or Pennsylvania (he doesn’t need them all) while avoiding any defections in Sunbelt states such as Arizona? The answer: With a flawed enough Democratic candidate, yes he can. If Democratic primary voters view Trump’s vulnerability as an opportunity to get all the ideological goodies they’ve ever wanted, rather than a rare chance to expand their coalition to moderate voters, they would again oppose a weak candidate with a weaker one. And they would re-elect the least fit president in American history.

Given the social and demographic trends of the country, it will soon be impossible to win a presidential election with an ethno-nationalist appeal. But we aren’t there yet. Meanwhile, Trump commits political vampirism — sucking the last remaining life from a dying coalition.

• Michael Gerson is a columnist for Washington Post Writers Group.