As it stands, the two people most likely to accept their parties' nominations at this summer's national conventions are Donald Trump and Hillary Clinton. Each has a sizable lead in delegates; each, we are assured by their opponents, will somehow end up losing. Those opponents, Ted Cruz and Bernie Sanders*, are hardly objective observers of the situation of course, any more than was Marco Rubio, whose last-minute insistence that he would win Florida was heartbreaking in the manner of an afterschool special. ("You'll get 'em next time, Tiger," we all sniffed. "You'll get 'em next time.") But it's an interesting...