Joe Biden’s limitations as a presidential candidate are so obvious that they’re almost a litany: He’s too old, too white, too male, too touchy-feely, too loquacious. But he has one huge plus: He may be the person who could move President Trump out of the White House.

Biden, the former vice president, rightly put the obligation of replacing Trump at the center of his announcement Thursday that he’s running. “The core values of this nation — our standing in the world, our very democracy, everything that has made America, America...