Before Tuesday night’s debate, the defining characteristic of the Democratic Presidential-primary race was Elizabeth Warren’s relentlessness. Warren’s campaign has covered, as she pointed out onstage, a hundred and forty town halls, twenty-seven states, and seventy thousand selfies. She has been the only candidate to dramatically change her prospects in the race, rising over the past year until she was leading in the betting markets, roughly even with the former Vice-President Joe Biden in the national polls, and edging ahead of him in Iowa and New Hampshire. Most significantly, Warren established the basic ethos of the Democratic primary: that it would be not only for the displacement of President Trump but also—in her awkward, effective phrase—“big, structural change.” (If that sounded both grand and a little hazy, so has the Democratic primary.) The tactical question going into Tuesday night was who might try to attack Warren, and how effective they might be. The deeper matter was to what extent the Democratic Party has remade itself in her image.

The moderators bored in on Warren early. Marc Lacey, the New York Times’ national editor, noted that Bernie Sanders had acknowledged that his Medicare for All plan would raise some taxes on the middle class. Lacey asked whether Warren, who supported the same plan, would make the same concession. She wouldn’t. She repeated what she called “my principles”: that costs would go up for corporations and the wealthy, and not ordinary Americans. But Sanders has suggested that Medicare for All will cost “more than thirty trillion dollars over ten years,” as Biden pointed out, in a country whose annual federal budget is less than five trillion dollars. A fireman and a schoolteacher making a hundred thousand dollars between them, Biden went on, would see their taxes go up by more than ten thousand dollars each year. Warren pivoted. She spoke of Americans who’d got sick, believing that they had good health insurance, only to watch as “the insurance company pulled the rug out from under them.” She described Medicare for All as the “gold standard,” and the only way to get health insurance to all Americans who needed it. But the more Warren circled back, explaining the way she saw the morality of the issue, the more plainly reluctant she seemed to say that big, structural change had a price tag, and that it might not be borne only by the billionaires. “At least Bernie’s being honest here,” Amy Klobuchar said. Pete Buttigieg addressed Warren more directly. “Your signature, Senator, is to have a plan for everything. Except this: no plan has been laid out to explain how the trillion-dollar hole in this Medicare for All plan . . . is supposed to get filled in.”

It was a good line, and Buttigieg had plenty of them. He is not always the most memorable debater, but he can hold both policy details and political positioning in his head at once, a rare skill. But there was a subtle shift in the campaign on Tuesday night, one that was not directly caused by Buttigieg but that may, in the end, benefit him. For most of the Presidential race, the candidates have positioned themselves for and against Bernie Sanders’s ideas, most often Medicare for All. Warren’s campaign has been tactically savvy in that she has sufficiently embraced Sanders’s expansive view of government in order to blunt the threat that he might have posed from her left (the tactics of a real pol, whatever her reputation as an idealist), while defining her campaign through an onslaught of policy.

But, as the twelve candidates onstage moved briskly past health insurance, the debate took on a different theme: not Biden versus Warren but Professor Warren versus the old Democratic Party. Kamala Harris chastised the debate moderators for a lack of attention to “women’s access to reproductive-health care, which is under full-on attack”—a reminder of how Democrats had often spoken about health care in the past. When Warren said that automation was not stripping jobs out of the Midwest (“The data show that we have a lot of problems with losing jobs, but the principal reason has been bad trade policy”), Cory Booker responded by speaking in favor of unions, a higher minimum wage, and the dignity of work—sturdy Democratic standbys.

It wasn’t an awful night for Warren. To her credit, she resisted joining Harris’s frankly alarming call for Twitter to suspend President Trump’s account, and yet ably used the example of the Consumer Financial Protection Bureau to argue that the structural change she seeks isn’t naïve. But, by evening’s end, she seemed a narrower candidate than she had at the beginning. When Warren was asked about the progressive plan to introduce a federal wealth tax, she said that the question should not be why she and Sanders supported the idea but why “everybody else on the stage thinks it is more important to protect billionaires than it is to invest in an entire generation of America.” That sounded overly defensive, especially since the billionaire Tom Steyer had just attacked the economic system as rigged toward the top. “Not even the billionaire wants to protect billionaires,” Klobuchar pointed out. When the topic turned to Syria, where Trump has withdrawn U.S. troops, leaving Kurdish allies to face a Turkish military offensive, Warren made a slightly philosophical point: “I don’t think we should have troops in the Middle East.” It fell to Buttigieg to defend the ethic of service, and the honor of allegiance. When he’d served in Afghanistan, he said, even the local janitors had put their lives on the line to support the American intervention. “I would have a hard time today looking an Afghan civilian or soldier in the eye,” he said.

Buttigieg ended the night in an interesting position. His campaign has been at once successful and a little formless; though his candidacy has risen from the fringe to the ranks of the plausible challengers, through his talent and ability to raise funds, his message is a little hard to discern. His pragmatic disposition is complicated by his efforts not to miss the boat on big, structural change—for instance, by backing an expansion of the Supreme Court. But his experience, as a military veteran in particular, extends to subjects that Warren’s simply doesn’t, and he is as good at drawing contrasts as anyone. “I don’t need lessons from you on courage, political or personal,” Buttigieg snapped at Beto O’Rourke, the subtext being that he had served while the Texan had not. Perhaps there is an opening for him as the candidate of the preëxisting Democratic Party rather than of those who would transform it. There is an opening for someone there, at least. Warren is the strongest candidate in the field. She also aims to hitch the Democrats to an agenda of sweeping economic transformation that the Party has not yet fully debated. Perhaps that began on Tuesday night. By the end, it didn’t seem like Warren’s party—not just yet.