John Locher / AP / Paul Spella / The Atlantic

Updated at 11:30 p.m. ET on June 27, 2019.

Joe Biden is the current front-runner of the Democratic Party. He’s leading all other primary candidates, in several polls, by double digits. And many party strategists believe that the working-class-whispering former vice president is the only candidate who can beat Donald Trump.

But at tonight’s Democratic primary debate, many of the questions posed—and some of the most heated moments—involved the candidate both physically and politically to Biden’s left: Bernie Sanders.

In one of the first exchanges of the night, the moderators cited Sanders’s affiliation with the Democratic Socialists of America, and asked former Colorado Governor John Hickenlooper whether the Democratic Party is veering toward socialism. Hickenlooper replied by criticizing two policy proposals that Sanders has famously championed: Medicare for All, which would usher in a government-run health-care system, and the Green New Deal, the ambitious blueprint to combat climate change. The moderate Hickenlooper, who took heat earlier this year for declining to call himself a capitalist, called for the candidates to more clearly communicate that “we,” meaning the Democrats, “are not socialists.” Senator Kirsten Gillibrand of New York cut in too, trying to assure viewers that the current debate within the party is not about socialism, but “between capitalism on the one hand and greed on the other.”

Several of the candidates seemed to define themselves against Sanders, reflexively comparing and contrasting their agenda with his. It was a reminder of just how popular the senator from Vermont’s ideas have become since his first campaign, in 2016: His policies have dominated discussion for much of the past three years, helping pry open the Democrats’ Overton window, inch by inch.

That’s especially true when it comes to health care. When asked about the pragmatism of progressives’ proposals, Senator Michael Bennet of Colorado said, “I agree with Bernie” on his goal of universal health care. But “where I disagree is on his solution of Medicare for All.” South Bend, Indiana, Mayor Pete Buttigieg, for his part, criticized what he sees as an impractical shift to a Medicare for All system. “Every person in politics who allows that phrase to escape their lips has a responsibility to explain how you are supposed to get from here to there,” Buttigieg said.

When the subject turned to student debt, the candidates jabbed at Sanders’s new proposal to cancel all Americans’ student debt, to the tune of $1.6 trillion, with no income or other restrictions. “I believe in free college for those whom cost could be a barrier,” Buttigieg said. “I just don’t believe it makes sense to ask working-class families to subsidize even the children of billionaires.” Biden explained that he would want to give students tuition-free community college instead.

The candidates, again and again, were playing the game on Sanders’s turf. He didn’t receive the Democratic Party’s nomination in 2016, and he might not secure it in 2020. But when the issues he’s long championed are being debated before 15 million Americans, in some ways he’s already won.

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