There was little doubt on Wednesday that Mr. Biden was more prepared and more polished than in the first debate, when he took a drubbing from Ms. Harris. He came armed with opposition research on her and Mr. Booker, and generally appeared more confident than last time.

His performance was uneven at times — and as several commentators noted, he was the only candidate to abruptly cut himself off, sometimes midsentence, when the moderators signaled he was out of time — but he easily cleared the low bar set by his last appearance.

“Excellent opening statement from @JoeBiden out of the gate. Rising above, focusing on Trump. General election attitude. It’s working.” — Adrienne Elrod, former senior adviser to Hillary Clinton “@JoeBiden finally played the card he should have played in the last debate when @KamalaHarris challenged him on race. @BarackObama vetted his record and nominated him for Vice President.” — Mr. Axelrod “Biden wobbling between strong moments — far better than Miami — and awkward stumbling.” — Mike Murphy, Republican consultant “Castro’s hit on Biden was a tough hit. But this is a different Biden from the one we saw in the first debate. In Miami, he looked rattled. Not tonight. He’s taking the hits and pushing back.” — Mo Elleithee, former spokesman for Mrs. Clinton and the Democratic National Committee

Harris was mostly on defense

Ms. Harris dominated the first debate from start to finish. That lifted her significantly in the polls, but it also meant that on Wednesday, she was as much a target as Mr. Biden. Where she had been on offense, she now found herself on defense.