THE FOURTH DEMOCRATIC primary debate, held just outside Columbus, Ohio on October 15th, packed 12 candidates onto a single stage. With that many egos and voices, it threatened to be shallow and fragmented. In fact, it was the most substantive debate yet—thanks largely to the unshowy, outstanding moderators, who asked pointed questions, held candidates to time, and knew precisely when to encourage and when to end one-on-one exchanges between the candidates. Nothing happened to alter the race radically, but the debate still revealed three things that will set the tone for the remainder of the primary campaign.

First, Bernie Sanders is not done. This was his first public appearance since his heart attack earlier this month, which dented his position in the polls. Many started to wonder whether a 78-year-old man had the stamina to campaign for another year, much less to lead America in his 80s. Those concerns remain valid, but he turned in a strong performance, aided by two qualities Mr Sanders shows infrequently. The first is warmth, evident when he thanked his fellow candidates for their well wishes. The second is a mischievous and precise comic timing, which he showed after Joe Biden gestured towards him while railing against Vladimir Putin. Mr Sanders asked if Mr Biden was “suggesting I’m Vladimir Putin?” and prompted what appeared to be a genuine embrace.

Mr Sanders also figured in the evening’s—perhaps the campaign’s—most important exchange. Mr Biden reminded viewers, as he has before, that he was “the only one on this stage who has gotten anything really big done”. Getting things done, he contended, requires “not being vague”—a quality that, after prompting, he assigned to Mr Sanders and Elizabeth Warren. In that he was only half right. The charge applies to Mr Sanders, who tends to shout rather than grapple with difficult policy questions, but not to Ms Warren, who has released dozens of detailed policy proposals.

Mr Biden really meant something closer to honesty: politicians should tell voters how they intend to pay for and pass their ambitious plans. Mr Biden contended that candidates must “level with people and tell them exactly what we're going to do, how we're going to get it done, and if you can get it done”. Ms Warren and Mr Sanders argued that their bold proposals would motivate voters more than Mr Biden’s centrism. Recent history suggests that Mr Biden is wrong. Donald Trump won by promising to build a wall and make Mexico pay for it, with no real plan to do either; eight years earlier Barack Obama won in part by promising a massive health-care expansion, which at the time seemed if not wholly unrealistic, then at least riskily ambitious. Governing, of course, requires making difficult choices, but voters seem to like boldness.

If that preference holds, then Ms Warren merits her front-runner status, and—the night’s second revelation—she defended it well. She rose in the polls having taken few direct attacks, perhaps because candidates thought Mr Biden a bigger threat, and perhaps because—having seen her cleanly eviscerate John Delaney in the debate in July—they were scared. This time around, Pete Buttigieg and Mr Biden—as well as Amy Klobuchar, Kamala Harris and Tulsi Gabbard, all trailing candidates searching for a spark—had their knives out, and Ms Warren fought back well. Mr Buttigieg scored an early hit when he accused Ms Warren of evasiveness for refusing to say whether Medicare for All would require raising taxes on the middle class. Mr Sanders, to his credit, said taxes would go up, but then echoed Ms Warren’s point, that overall health-care costs would decline because there would be no more premiums or co-pays. Ms Harris tried to goad her into a pointless and petty debate over whether Twitter should suspend Mr Trump’s account; Ms Warren brushed her off without breaking stride. Ms Warren set the tone on the threat posed by big tech firms, even if none of the other candidates were as excited to break them up as she was.

Ms Warren remains a long way from victory. She is vulnerable on implementation questions; voters may rally to boldness, but at some point rubber and road must meet. And she is, as Mr Buttigieg pointed out, deeply evasive on health care—the one area in which she has not released a detailed plan, preferring simply to reiterate her support for Mr Sanders’s Medicare for All bill. Her equivocating is probably a ruse to afford her maximum maneuverability through the rest of the primary campaign and the general election. Last, she seems to offer a sort of Trumpism for the left, with greedy corporations rather than elites and illegal immigrants as the all-purpose villain. Mr Biden remains her most formidable challenger. She has yet to cut meaningfully into his support among blacks, and there is probably a far larger constituency for his familiar moderation among general-election voters which neither she nor the Democrats should wish away.

But—the night’s third takeaway—Mr Biden’s position is not what it was. Mr Buttigieg, Ms Klobuchar and Cory Booker all turned in strong performances that seemed informed by a sense that Mr Biden’s lead is shakier than polls suggest. They positioned themselves as alternatives in his moderate lane. Mr Buttigieg was particularly good in the debate’s foreign-policy section. It helped that in Tulsi Gabbard—who falsely accused America of waging a “regime-change war” in Syria, and blamed America for the Syrian refugee crisis—he had a contemptible foil.

The irony is that Mr Biden may have turned in his strongest debate performance yet. That is a low bar. He still managed one bizarre reference to a person “clipping coupons in the stock market” but overall he seemed more poised, focused and less prone to rambling than in previous debates. But Ms Warren is no longer nipping at his heels; she is running level or ahead of him. Nothing that happened during the debate looked likely to alter that trajectory. That should worry Mr Biden.