Psychologist John Gottman said that nothing is so destructive to a marriage as contempt. Couples can come back from many sorts of conflicts, but not festering disgust — a sense, by one or both people, that the other is beneath them. That’s why, if blue and red America were spouses, the relationship would look hopeless. Call it irreconcilable differences.For at least the last decade, a florid, aggressive contempt has been a constant in our politics. Donald Trump, after all, doesn’t just shower liberal cities and states with insults (and, in a demented artificial intelligence video he posted, with excrement). His...