As Donald Trump is learning, it is difficult to go full-on dictator in a democracy. When Lord Haw-Haw’s voice came crackling across the radio during World War Two, no one in Germany was questioning Hitler’s use of an upper-class Brit to spread his Nazi propaganda. The Cambodians didn’t ridicule Pol Pot for murdering intellectuals with soft hands, and Kim Jong-il can say he was born under a shining star and a rainbow on a sacred mountain without any North Koreans invoking the equivalent of a 25th Amendment. Trump has done many crazy things in the first year of his second...