President Donald Trump arrives at Election Day on Tuesday toggling between confidence and exasperation, bravado and grievance, and marinating in frustration that he is trailing Joe Biden, whom he considers an unworthy opponent. “Man, it’s going to be embarrassing if I lose to this guy,” Trump has told advisers, a lament he has aired publicly as well. But in the off-camera version, Trump frequently exclaims, “This guy!” in reference to Biden, with a salty adjective separating the words. Trailing in most polls, Trump has careened through a marathon series of rallies in the past week, trying to tear down Biden...