If Mr. Trump is removed via impeachment and conviction — that is, with those 20 Republican votes — Republicans can say, “See, we’ve come to our senses; got that out of our system.” But if they renominate Mr. Trump and stick with him through November 2020 and the voters clearly say no, not again, Republicans are left sitting in the wreckage. They will be trying to air out the Trump stench for a generation, maybe two, which is precisely the fate they deserve.