REPUBLICAN lawmakers have seen the Trump disaster coming for a while now. They simply have no clue what to do about it.

A couple of months ago — before we learned that Donald Trump Jr. wanted to spend quality time with people he believed represented the Russian government, before the president publicly humiliated his attorney general and was abandoned by top business executives, before he claimed “some very fine people” were marching in Charlottesville, Va., alongside neo-Nazis and white supremacists — a Republican member of Congress I spoke with called the president a “child king,” a “self-pitying fool.”

Even then, the words that came to mind when some congressional Republicans described the president were “incompetent” and “unfit.” There were concerns about his emotional stability. “There’s now a realization this isn’t going to change,” one top Republican aide on Capitol Hill said. Yet there is the simultaneous realization, as a House member told me when talking about Republicans in their home districts, that “we’re never going to have a majority of people against him.”

Maybe, but for now this presents Republican members of Congress who are privately alarmed by Mr. Trump with a predicament. Regardless of what he does, a vast majority of his core supporters are sticking with him. A recent Monmouth University poll found that of the 41 percent of Americans who currently approve of the job he’s doing, 61 percent said they cannot see Mr. Trump doing anything that would make them disapprove of him. Mr. Trump was on to something when he said in January 2016, “I could stand in the middle of Fifth Avenue and shoot somebody and I wouldn’t lose voters.”