Just before Tuesday night’s Democratic debate began, CNN’s Jeff Zeleny said on air that the Bernie Sanders campaign wanted its candidate to be more “present” than he was during the first debates, in June. In retrospect, it was a strange thing to worry about. It took more than forty minutes for the debate to move to any topic other than Sanders’s signature issue, Medicare for All. Sanders had enough time to tally the number of Americans going bankrupt each year because of medical bills (five hundred thousand, more or less) and the amount of money that the health-care industry has spent on lobbying. CNN’s video introduction had, a little stagily, teased a fight between Sanders and Elizabeth Warren (“they’re fighting for the same cause—and the same voters”), but, when Sanders denounced the health-care industry’s political influence (it spent four and a half billion dollars on lobbying and campaign contributions during the past twenty years, he said), Warren nodded emphatically. Later, when Warren sounded a protectionist note on trade, Sanders returned the favor: “Elizabeth is absolutely right.” Present? Progressive ideas were the whole debate.

Maybe this was because the two marquee progressives, Sanders and Warren, were the best communicators. The moderates came with slogans: “Wish-list economics,” Steve Bullock, the governor of Montana, said. “Fairy-tale economics,” John Delaney, a former congressman from Maryland, said. Warren shot back: “I don’t understand why anyone goes to all the trouble of running for President of the United States to tell us what we can’t do and shouldn’t fight for.”

Warren sounded different from the other candidates: her imagery was more specific. She told the story of Ady Barkan, a health-coverage activist, who is dying of A.L.S. and who has insurance that does not cover his bills. Warren said, “He talks about what it’s like to go online, with thousands of others, to beg friends, family, and strangers” for cash. Her language was alive. The rigged system had not just propped up the wealthy and connected but “kicked dirt in the face of everyone else.” The insurance companies have “sucked billions out of the health-care system” and stored them as profits. “We aren’t going to solve the problem by being the party of small ideas and spinelessness,” she said. “We’re going to solve them by being the Democratic Party of big, structural change.” It was hard for anyone to find a comeback to that.

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The luck of the draw meant that none of the more moderate candidates on the stage could match Sanders’s or Warren’s profile. Even Beto O’Rourke and Pete Buttigieg seemed a little shy about drawing distinctions with the two contenders to their left. Often they sounded merely like paler versions of them. Did O’Rourke believe that the government should fund tuition-free four-year college? “I support free two-year college,” he said. But, when he tried to criticize Sanders’s and Warren’s Medicare for All plan, which would eliminate private health insurance, he couldn’t quite bring himself to name his rivals: “The two senators to my right,” he said. Buttigieg got a loud burst of applause for saying, “If we embrace a far-left agenda, the Republicans will call us a bunch of crazy socialists. But, if we embrace a centrist agenda, they will call us a bunch of crazy socialists.” It was a good line. But he was making Sanders’s point for him.

A half hour before the debate started, the Greater Detroit Democratic Socialists of America marched along Woodward Avenue, carrying banners and signs bearing the D.S.A.’s red rose and calling for the Green New Deal. In the midterm elections, Democratic candidates won votes in moderate suburban districts across the country, and with them a broad national majority, by effectively portraying the Republicans as radicals—the party of Obamacare repeal and child separation—and themselves as defenders of the way that things had been. The simple news tonight was that Warren moved the Democrats a bit further from the party of the 2018 midterms, and a bit closer to the activists in the streets. The subtler development was that she altered the direction of the progressive left, so that it no longer pointed so directly at a utopian socialism but to the oppositional work of what she called “big, structural change.” That’s the revolution now. Over to you, Kamala Harris and Joe Biden, on Wednesday night.