Donald Trump has a knack for making his most committed apologists look like complete imbeciles—even if they are not complete imbeciles, though many of them are. This has been true for several years. But in recent weeks, Trump’s trickle-down idiocy has become a significant midterm-election issue for Republicans, and a drag on some of the party’s most vulnerable Senate candidates.If you’re a candidate seeking a GOP nomination, Trump’s blessing can be a political wonder drug. But it comes with debilitating side effects.