DETROIT — The leading liberal populists in the Democratic presidential primary, Senators Bernie Sanders and Elizabeth Warren, strenuously fought back against accusations of impracticality and warnings of electoral ruin on Tuesday night, as a group of moderate underdogs sought to dent their momentum in the second round of presidential primary debates.
From the first moments on the debate stage, there were charges of “wish-list economics” and critiques of “massive government expansions” as the candidates engaged in an unusually substantive discussion of health care policy. Gov. Steve Bullock of Montana, appearing in a debate for the first time, took implicit aim at Mr. Sanders by insisting that distressed farmers and teachers could not “wait for a revolution.” And former Representative John Delaney of Maryland conjured electoral catastrophes of the past to argue that the activist left could not be trusted to lead the party.
The course recommended by Mr. Sanders and Ms. Warren, Mr. Delaney said, was defined by “bad policies like ‘Medicare for All,’ free everything, and impossible promises that will turn off independent voters and get Trump re-elected.”
Mr. Sanders and Ms. Warren responded with defiance, rejecting the moderate candidates as offering policies that were plainly unequal to the political moment. Without taking aim at her more centrist rivals by name, Ms. Warren used her opening statement to dismiss their ethos of incremental change.
“We’re not going to solve the urgent problems that we face with small ideas and spinelessness,” Ms. Warren said.
Mr. Sanders, who has largely staked his candidacy on his support for single-payer health care, defended the policy ferociously, at one point accusing a CNN moderator, Jake Tapper, of using a “Republican talking point” when raising questions about his plan, and then noted that “the health care industry will be advertising tonight on this program.” Prompted to address Mr. Delaney’s criticism of “Medicare for All,” Mr. Sanders fired back laconically: “You’re wrong.”
Assailing the instability of the current health care system, Mr. Sanders argued, “The answer is to get rid of the profiteering of the drug companies and the insurance companies.”
Mr. Sanders and Ms. Warren have largely defined the party’s conversation about policy up to this point, and there were signs of impatience on the debate stage with the admonitions of moderates about how Republicans might brand Democrats in the general election as outside the political mainstream.
Mayor Pete Buttigieg of South Bend, Ind., drew applause with the prediction that Republicans would brand the eventual Democratic nominee as a wild-eyed extremist no matter what policies that person endorsed.
“Let’s just stand up for the right policy,” said Mr. Buttigieg, who has endorsed a liberal health care policy more modest than the one favored by Ms. Warren and Mr. Sanders.
The same center-versus-left divide evident on health care was also on display as the candidates clashed over immigration and whether some of the proposals offered by the liberal candidates would represent a boon to President Trump’s re-election.
“We got a hundred thousand people showing up at the border right now,” said Mr. Bullock. “If we decriminalize entry, if we give health care to everyone, we’ll have multiples of that.”
Turning to Ms. Warren, he accused her of “playing into Donald Trump’s hands” for wanting to make illegal migration a civil penalty and seeking to provide federal benefits to undocumented migrants.
Ms. Warren fired back that “seeking refuge, seeking asylum” is “not a crime.”
Representative Tim Ryan of Ohio also criticized his progressive rivals for what he described as overly permissive immigration proposals. “If you want to come into the country you should at least ring the doorbell,” said Mr. Ryan.
The Tuesday debate did not feature any of the candidates of color — they will all be onstage Wednesday — but it marked the first opportunity for half the field to speak about President Trump’s recent spree of derogatory attacks against a group of minority lawmakers, an offensive that has appalled Democrats and much of the country. Several of the candidates harshly criticized the president in their one-minute opening statements, with Ms. Warren saying that any one of the Democratic contenders on the stage Tuesday or Wednesday would be a vast improvement over Mr. Trump.
Within the primary, the Detroit forum represented strikingly different opportunities for the two tiers of candidates: The three leading figures Tuesday — Ms. Warren, Mr. Sanders and Mr. Buttigieg — had a chance to maneuver carefully, while others were facing pressure to pursue more impatient risk-taking that might elevate their candidacies.
Seven of the debaters, five of them relatively moderate white men, have been struggling to attract interest in the race and Tuesday’s forum may be their last chance to break through until the third debate in September, when the requirements for participation will be far higher.
For several Democrats, including former Representative Beto O’Rourke of Texas, Mr. Bullock and former Gov. John Hickenlooper of Colorado, the debate had the potential to become a decisive moment. All three men have fielded entreaties from Democratic leaders to leave the presidential race and run instead for the Senate in 2020, and in Mr. Hickenlooper’s case some of his closest associates have urged him to do just that.
Under pressure to grab media attention, Mr. Hickenlooper sought to pick a fight with one of his far better-known rivals on the eve of the debate: Ms. Warren, he warned on Twitter, had “big ideas that have an even bigger cost.”
“We proved in Colorado that you don’t need big, expensive government programs to achieve progressive goals,” he tweeted.
One of the avenues the more centrist candidates could have for highlighting their differences appeared to have been pre-emptively blocked by the debate organizers, though: CNN said it would not ask yes-or-no questions or ask for a show of hands, the sort of queries that in the first debate illustrated the leftward shift of the party.
The most important political rivalry in the debate — between Ms. Warren and Mr. Sanders — was not guaranteed to produce a dramatic clash. In general, the two have been more inclined to defend their shared ideas against centrists like Mr. Hickenlooper, than to attack each other over their real but comparatively modest policy differences.
Though the two liberal populists are competing for some of the same primary voters, they both indicated in the run-up to the debate that they were not eager for direct combat. In addition to sharing a personal friendship, Ms. Warren and Mr. Sanders could also face significant backlash from each other’s supporters from an aggressive confrontation.
Further, Mr. Sanders and his aides are more eager to confront Joseph R. Biden Jr., who they view as the most formidable moderate in the race and who also is currently winning support from many of the working-class voters they covet.
For her part, Ms. Warren has sought to both flatter Mr. Sanders and protect her left flank by offering a full-throated embrace of Mr. Sanders’s “Medicare for All” legislation. “I’m with Bernie,” she has repeatedly said. Of the leading candidates, Ms. Warren is the only one besides Mr. Sanders to lend her full support to the plan.
Still, there are differences between the two in substance, attitude and political strategy. Ms. Warren has risen rapidly in the polls by both pulling away support from Mr. Sanders among younger and more liberal voters, and winning over many women — especially educated white women — who tended to support Hillary Clinton in the 2016 primaries. She has generated a wider array of policy proposals than Mr. Sanders, usually taking greater pains to explain how they would be paid for and at times limiting the generosity of the public benefits she has proposed, as in the case of student loan forgiveness.
Mr. Sanders has seen his support erode since the 2016 election, but remains highly popular among very liberal Democrats and maintains a following among working-class whites that Ms. Warren has not yet matched. He has staked his campaign, above all, on his support for single-payer health care, and he has taken a more combative approach than Ms. Warren to candidates whom he sees as overly accommodating of the wealthy’s interests — Mr. Biden chief among them.
[We tracked down the 2020 Democrats and asked them the same set of questions. Watch them answer.]
Signaling that Ms. Warren was not his focus, Mr. Sanders spent the weekend before the debate targeting Mr. Biden and Senator Kamala Harris of California for health care policies he denounced as inadequate and deferential to corporate power. But Mr. Biden and Ms. Harris will not appear on the debate stage until Wednesday, when the seething rivalry between them that began in the first round of debates may again be on vivid display.
Mr. Buttigieg, a distant third in prominence among the debaters, has needed a jolt of energy for his campaign: While he has raised an enormous sum of money, more than any other candidate in the last fund-raising quarter, his polling numbers have steadily slipped into the mid-single digits over the last month. A liberal reformer rather than an economic populist, Mr. Buttigieg has ample areas of disagreement with Ms. Warren and Mr. Sanders, on issues such as health care and higher education.
Similarly situated in the debate, if not in the polls, was Senator Amy Klobuchar of Minnesota, an avowed moderate who has been touting her appeal across the Upper Midwest states that are likely to decide the general election. Ms. Klobuchar has profound disagreements on policy with the leading candidates in the Tuesday debate, calling for measured improvements to the health care and education systems rather than sweeping legislation, and rebuffing a number of liberal litmus tests on subjects like immigration.
In theory, a debate stage in swing-state Michigan would be an ideal setting for laying out those differences. Up to this point, however, Ms. Klobuchar has stopped well short of calling out Mr. Sanders or Ms. Warren by name about their differences. In their first debate encounter last month, Ms. Klobuchar passed up several opportunities to draw clear distinctions and she has similarly declined to do so in appearances since the Miami forum.