Biden bear-hugged Obama. His foes couldn’t pry him loose.

The former VP got one big thing right on the debate stage. And that may be all that mattered.

Historically, when a former vice president runs for a promotion to the top job, he struggles with the legacy of his former boss. George H. W. Bush was caricatured as a wimp as he tried to step out of Ronald Reagan’s shadow. Al Gore was paralyzed as he tried to embrace Bill Clinton’s popular policies while distancing himself from the sex scandal that led to Clinton’s impeachment. Hillary Clinton faced a...