Jordan Gale / The N​ew York Times / Redux

Updated at 10:40 a.m. ET on January 15, 2020.

The two most liberal candidates drove the conversation at last night’s Democratic presidential debate, but in a manner that underscores the challenge each may face in building a coalition across the party’s ideological divides.

Bernie Sanders and Elizabeth Warren, the two senators jostling for the support of the Democrats’ most progressive voters, both delivered confident, aggressive performances in which they underlined their commitment to an array of liberal causes, from withdrawing all American forces from the Middle East to raising taxes on the rich and opposing most free-trade agreements. The debate made clear that they are both banking on winning the nomination much more by consolidating the party’s most liberal flank than by extending their appeal across all of its ideological and political factions. “This is the moment when we have got to think big and not small,” Sanders insisted in his closing statement, in words that summarized as well the argument from Warren.

None of the more centrist candidates on the slimmed-down debate stage was nearly as vivid. And overall, the debate lacked the intensity that many expected for the final confrontation before the first votes are cast in Iowa, on February 3—especially since recent polls have shown the top four candidates all closely bunched together. The evening’s most anticipated moment largely fizzled, too. Sanders flatly denied that he told Warren, during a private meeting in 2018, that he believed a woman could not win the presidency, as initially reported by CNN. And when asked about Sanders’s denial, Warren chose not to challenge him—detouring instead into a forceful argument for why women can win elections. Without a genuine confrontation between the two, the real fulcrum of the debate was the division between the two of them and former Vice President Joe Biden, former Mayor Pete Buttigieg, and Senator Amy Klobuchar of Minnesota.

Yet the same unwavering conviction that helped Warren and Sanders stand out onstage underscored the gamble each is taking: that purism can prevail in a Democratic primary electorate that is more ideologically diverse than often assumed.

A cumulative CNN analysis of all the exit polls conducted in the 2016 Democratic primary found that only one-fourth of voters in that contest, between Sanders and Hillary Clinton, identified as “very liberal”; just over one-third called themselves “somewhat liberal”; and the remaining two-fifths identified as “moderate” or “conservative.” While Sanders broke even with Clinton among the voters who identified as very liberal, she won a 56 percent majority of the somewhat-liberal voters and more than 60 percent of the moderates.

The Iowa caucuses tend to attract an electorate more liberal than Clinton’s cohort: In 2016, according to the media entrance polls conducted at the time, only about one-third of caucus-goers identified as moderate or conservative, while nearly three in 10 identified as very liberal and four in 10 identified as somewhat liberal. These results help explain the tack Warren and Sanders took in their presentations last night. Yet beyond Iowa, the Democratic primary electorate in many states is much more centrist, especially across the South and Midwest: For instance, in Texas, Michigan, and Ohio, each of which votes in early March, the 2016 exit polls found that only about one-fifth of voters identified as very liberal, while roughly twice as many called themselves moderate or conservative.

Both Warren and Sanders are relying heavily on the party’s most liberal quarters, polls suggest. In this week’s Quinnipiac University national survey, Warren drew 38 percent of Democratic voters who identified as very liberal but only 7 percent of moderates and conservatives; for Sanders, the numbers were 24 and 14, respectively. Biden’s support, by contrast, followed the inverse pattern: He won 29 percent of the moderates and conservatives, but only 15 percent of those who identified as very liberal.

At the debate, Warren didn’t show much inclination to reach beyond her base—and Sanders showed even less to reach beyond his.

From his very first answer, Sanders planted his flag on the left flank of the party’s internal ideological debate by responding to a question about his credentials to serve as commander in chief by stressing his opposition to the war in Iraq. Sanders reiterated his determination to remove all American troops from the Middle East and delivered a sweeping condemnation of military intervention abroad: “The American people are sick and tired of endless wars that have cost us trillions of dollars,” he said. On trade, Sanders separated himself from all his major rivals by reiterating his opposition to not only the North American Free Trade Agreement approved under President Bill Clinton, but also the updated agreement with Mexico and Canada that the Democratic House recently voted to approve. Sanders dodged a question about the estimated $60 trillion cost of his entire agenda, instead retreating to familiar arguments about why he believes a single-payer system will benefit American families. He would not even offer an estimate on the cost of single-payer alone, which the center-left Urban Institute has projected would be $34 trillion over the next decade, more than the government spends on Medicare, Medicaid, and Social Security combined.

Warren was only a half-step behind. While she defended the new deal with Mexico and Canada, she expressed general skepticism about free trade, unequivocally urged the removal of American troops from the Middle East, touted a plan for government to manufacture its own pharmaceuticals, and stressed her determination to confront “giant corporations” and the wealthy.

Both Warren and Sanders argued that Democrats can beat Donald Trump only by offering such an unwavering agenda, which they maintain can spur massive turnout. “The only way we beat Trump is by a campaign of energy and excitement, and a campaign that has by far the largest voter turnout in the history of this country,” Sanders declared at one point. As they have before, the more centrist candidates argued that the party needs an agenda that would speak to a broader coalition of voters.

But none of them delivered that case with as much conviction and energy as the two leading liberals on the stage. Biden, in particular, vanished for much of the debate; until his closing statement—which featured a strong appeal to reclaim the American character from Trump—it seemed unlikely that viewers would remember much of what he said. (While the Los Angeles debate last month dampened concerns among many Democrats about Biden’s capacity to build a case against Trump in the general election, last night’s performance seems destined to rekindle them.) Klobuchar and Buttigieg were better at making the case against the ideas from the left, particularly single-payer, though neither was as effective as they had been in earlier encounters.

The past four Democratic winners of the Iowa caucuses (Al Gore in 2000, John Kerry in 2004, Barack Obama in 2008, and Hillary Clinton in 2016) won the nomination, even when New Hampshire favored a different candidate. There’s reason to believe that the state might not be as decisive this time, largely because all the leading candidates there, apart from Biden, are struggling with African American voters, who were crucial to the winning coalitions assembled by the recent Iowa winners. But there’s no question that Iowa is poised to exert a huge sorting impact on the race, framing the top of the field and possibly dooming most of the remaining candidates.

With such stakes on the table, the candidates chose last night—surprisingly—to largely pass on their final opportunity before the vote to try to change voters’ perception with a single dramatic moment. Warren’s identification with the frustration so many women feel about having their qualifications questioned made her the single candidate most likely to receive a late boost from the evening. But mostly, less than three weeks before voting finally begins, all the candidates appeared content to play the cards they’re already holding. For Warren and Sanders, that means trying to win the nomination by rallying a base that is the party’s most vocal faction, but also, historically, far from the largest.

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