During a verbose half-century in public life, Joe Biden has never made such a succinct case for his election.

“Ask yourself,” he said in Pennsylvania on Monday, “Do I look like a radical socialist with a soft spot for rioters? Really?” In 16 words — the last one delivered with a thespian frown — the US Democratic presidential hopeful alluded to a long career of moderation. The Republican friends. The orthodox foreign policy. The prison-building crime bill. There is no less plausible Jacobin in the party.

Everything about the line was perfect, in fact, except its necessity. Two months away from an election, a candidate should not have to distance himself from political violence. As deftly as he did it, one of Washington’s old saws — “If you’re explaining, you’re losing” — feels dangerously apt.