Last week Mr. Obama was weirdly passive. Last night Mr. Biden was weirdly aggressive, if that is the right word for someone who grimaces, laughs derisively, interrupts, hectors, rolls his eyes, browbeats and attempts to bully. He meant to dominate, to seem strong and no-nonsense. Sometimes he did—he had his moments. But he was also disrespectful and full of bluster. "Oh, now you're Jack Kennedy!" he snapped at one point. It was an echo of Lloyd Bentsen to Dan Quayle, in 1988. But Mr. Quayle, who had compared himself to Kennedy, had invited the insult. Mr. Ryan had not. It...