Only an idiot would predict tonight’s midterm results. So let me oblige
If a midterm is a referendum on a presidency, it is one that presidents usually lose, especially Republican presidents. Since the Civil War, the president’s party has gained seats one only three occasions: 1934, 1998 and 2002. Only on the last of those was recipient of the public’s inexplicable affection was a Republican president, in this case George W. Bush. And in that instance the public’s affection was explicable in the aftermath of the 9/11 attacks. So yes, Republican losses tonight will constitute a diminution of Donald Trump’s presidency. The question is not one of nature but of degree. Will the diminution resemble a mild paddling of the kind that a pornographic actress might perform on the presidential backside with a rolled-up magazine?