OK, Elizabeth Warren had the best one-liner of the night when challenged about being the oldest president ever, she answered, “I’d be the youngest woman ever inaugurated.”

And, OK, the dust-up between Amy Klobuchar and Pete Buttigieg on his alleged insult to senatorial experience and his puny political clout will likely be the most featured video bites of the debate.

But the most significant story of the most intense, substantive debate of the 2020 Democratic cycle is that Joe Biden—an almost default frontrunner who has managed to stumble at one point or another in each of the past debates—may have finally found his footing in an environment where he has demonstrated persistent discomfort.

In a Democratic primary that has often sounded like a battle for the hearts of the progressive blogosphere, with candidates outdoing themselves to spin out the most inclusive, greenest, most redistributed vision of America, Biden has often felt like a throwback—a visitor from Obamaworld and other vanished lands who has trouble parrying attacks from sharper and fresher voices.

In Thursday's debate, however, Biden consistently demonstrated the capacity not just to defend himself but to turn that defense into effective arguments for his candidacy.

There’s a reason Biden is running first in the polls: He has the old-fashioned centrist segment of the party largely to himself, and a lot of Democrats see him as the party’s best chance against Trump. But it’s been hard to articulate that as a constructive philosophy. In past debates, for instance, Biden’s insistence that he could find common ground with Republicans has left him wide open to the charge that he was either blind to Republican scorched-earth politics or living in an irrelevant past of long-lost comity.

Thursday, he issued an answer to that, using the very acts of the Trump administration that have led to impeachment—the attempt to get Ukraine to question his integrity—in making his case.

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“If anyone has reason to be angry with the Republicans and not want to cooperate, it’s me — the way they’ve attacked me, my son, my family,” he said. “I have no love.” That fact, an argument that placed Biden right at the heart of the entire Democratic case against President Donald Trump, gave power to his refusal "to accept the notion as some on this stage do that we can never, never get to a place have we have cooperation again.”

When asked about his age and whether he’d pledge to run for a second term, he said—after bantering with moderator Tim Alberta—“No, I’m not willing to commit one way or another. Here's the deal: I'm not even elected one term yet, and let's see where we are. Let's see what happens. But it's a nice thought.” It was an answer grounded in plausibility; how can anybody know where any of us will be in four years?

When he was asked about Hong Kong and China, his response sounded like a candidate with a grasp of geopolitics.

“We are going to be there to protect those folks,” he said. “Secondly, we, in fact, should make sure we begin to build our alliances, which Trump has demolished with Japan and South Korea, Australia and Indonesia. We, in fact, need to have allies who understand that we’re going to stop the Chinese from their actions. We should be going to the U.N. immediately and seek sanctions against them in the United States for what they did. … We're not looking for a war. But we have to make clear, we have a Pacific power, and we’re not going to back away.”

And when the inevitable “Medicare for All” argument surfaced again—a topic that has trapped one debate after another in an almost unwinnable battle of nitty-gritty policy distinctions—Biden had a planned attack designed, very effectively, to unapologetically distance himself from an issue that much of the left has embraced. He pushed back hard against Bernie Sanders’ claim that the average worker would be in better financial shape under the plan.

Your plan would "cost $30 trillion,” he said, theatrically claiming the stage for his moment. “Let’s get that straight. $30 trillion over 10 years. Some say it costs $20 trillion. Some say it costs $40. The idea that you’re going to be able to save that person making $60,000 a year on Medicare for all is absolutely preposterous. Sixteen percent of the American public is on Medicare now, and everybody has a tax taken out of their paycheck now. Tell me, you’re going to add 84 percent more and there’s not going to be higher taxes? At least before he was honest about it. It's going to increase personal taxes.”

Sanders had a reply ready, and the point here is not that Biden won the argument: It’s certainly debatable whether the average worker would be better off paying more money in taxes or more in insurance premiums. The point is that Biden had an argument—one that combined coherence and a politically potent theme—that was often missing in past debates.

As for the fundamental argument for Biden’s candidacy—that at the end of the day, he’s the guy who can take on Trump—he saved that one for last. In his closing statement, yes, he blurred the names of various pieces of legislation, but nailed it with one slow and clear rhetorical question, delivered with genuine focus, about beating Trump: “Who is the one most likely to do that?”

The post-debate analysis will likely—and accurately—note that Klobuchar went hard after Buttigieg because Iowa is her first and last chance to emerge as a serious series contender, and that it’s Buttigieg, not Biden, who sits atop the Iowa polling.

But Biden did something he needed to: He confidently cleared a space around his own policy ideas, and his own candidacy, that remained almost entirely unchallenged by the rest of the field. If Thursday's debate is not a “one-off”—if Joe Biden has found his footing at the moment he really needs to, as the field is winnowing and the campaign hits primary season at full speed—that may well be the most politically significant story of the night.