Pete Buttigieg and Elizabeth Warren are the shiny objects.

Joe Biden just may be the keepsake that endures.

The other two went at it on Thursday night, quarreling over the meaning and morality of a wine cave, in an exchange that distilled the Democratic primary’s broader tension between pragmatism and purity, compromise and idealism. Biden was careful not to be drawn too far into it and, during other stretches of the debate, stood back.

Why wouldn’t he? For all the worry because he sometimes stutters, for all the concern because he occasionally sputters, for all his corny locutions (“malarkey”) and reflexive conversation fillers (“here’s the deal”), the former vice president has almost consistently maintained a lead over his Democratic rivals in national polls since he announced his candidacy last April. He has recently gained ground in Iowa, the state that votes first, meaning that he may avoid what had been looking like a candidacy-imperiling embarrassment there.

He has survived salvos from critics and messes of his own that were supposed to halt or at least hobble him: the attention to his crossing-the-line physicality with women; the flip-flop about public funding of abortions; the back-and-forth with Kamala Harris about busing; the moment at the fifth Democratic primary debate when he seemed to forget either that she was in the Senate or that she was black.