DETROIT—Bernie Sanders has a succinct message for Democrats who think that his landmark “Medicare for All” proposal is politically impossible: “You’re wrong.”

In the first question posed at the Democratic presidential debate here on Tuesday evening, the Vermont senator and progressive icon issued that two-word response to a question posed by moderator Jake Tapper, who pointed out that fellow candidate Rep. John Delaney had dismissed the expansion of Medicare for all American citizens as “political suicide.”

Sanders, an independent who caucuses with the Democrats and who has demonstrated remarkable resilience despite months of attacks for his support of democratic socialism, noted that Canada and its expansive social safety net exists a mere five minutes from the Fox Theatre in downtown Detroit, adding that millions of Canadians use a “Medicare for All”-esque system without leaving medical visits burdened with debt.

“Health care is a human right—I believe that,” Sanders said, to exuberant applause from members of the audience.

He was soon joined by Sen. Elizabeth Warren (D-MA), who backed up Sanders calling the criticisms of the healthcare overhaul “Republican talking points.”

“Let’s be clear about this, we are the Democrats. We are not about trying to take away health care from anyone,” she said. “That’s what the Republicans are trying to do and we should stop using Republican talking points in order to talk with each other about how to best provide that health care.”

The defiant statement kicked off a lengthy debate over the merits of Medicare for All, that soon pitted Warren and Sanders against the other contenders on stage who expressed support for less drastic changes to the health care system.

Montana Governor Steve Bullock, who was appearing on the debate stage for the first time, said he would oppose “any plan that rips away quality health care from individuals.” “This is an example of wish list economics,” he said.

Mayor Pete Buttigieg, who does not support eliminating private insurance, said the concern should lie in supporting the right policy—which he calls “Medicare for All Who Want It” and involves improving the ACA rather than scrapping the current system—and not what Republicans may say.

“It’s time to stop worrying about what the Republicans will say,” he said. “If [we embrace] a far left agenda, they will say we’re a bunch of crazy socialists,” he said. “If we embrace a conservative agenda agenda, they will see we’re a bunch of crazy socialists. Let’s stand up for the right policy, go up there and defend it.”

Sanders retorted, “Let’s be clear what this debate is about, nobody can defend the dysfunctionality of the current system. What we are taking on is the fact that over the last 20 years the drug companies and insurance companies have spent billions of your health insurance money by lobbying and campaigning contributions.”

A few moments later, after former Colorado governor John Hickenlooper expressed a more incremental approach to expanding Medicare, Warren was quick to reject it.

“We have tried this experiment with the insurance companies,” she began. “And what they’ve done is they’ve sucked billions of dollars out of our health care system. And they force people to have to fight to try to get the health care coverage that their doctors and nurses say that they need.”

She concluded, “That’s what we have to fight.”

The exchange again highlighted the divide between the current crop of candidates, many who are under increasing pressure to seize opportunities, or, failing that, force relevance as a much higher hurdle to qualify for the next series of debates in September looms.

Although the lineup of Tuesday’s debate is the result of a randomized shuffle of top-, mid- and bottom-tier candidates, the first of this week’s two debates is expected to lean disproportionately towards delineating policy differences between the candidates. Sanders of Vermont and Elizabeth Warren of Massachusetts are sharing both center stage and a similar lane in the race for the Democratic presidential nomination, crashing what could otherwise be deemed “Moderate’s Night” at the Fox Theatre.

Although the pair share numerous policy priorities—as well as home-state media markets with the crucial primary state of New Hampshire—their stylistic differences in a debate setting were expected to paint a distinction on Tuesday.

Sanders, who has never failed to find an opportunity to redirect a question towards his core message of economic equality, had signaled in the past few days that he’s not interested in preparing for stage combat with Warren, even on his signature “Medicare for All” proposal—although his two-word response to criticism of the plan indicates that he’s more than ready to defend it.

Warren, for her part, has been rising in both fundraising and polling since last month’s debate, and could use the debate as a platform to broaden her appeal from her left-leaning base.

Brewing just to either side of Sanders and Warren is another anticipated “match-up” between former Texas congressman Beto O’Rourke and Pete Buttigieg, the mayor of South Bend, Indiana who has largely usurped O’Rourke’s position as a media darling. Buttigieg, who outraised nearly every other candidate last quarter, is still facing criticism for his handling of a fatal police shooting in the city he runs.

O’Rourke needs to peel off some of Buttigieg’s “rising star” support if he hopes to recover from disappointing fundraising numbers and cratered polling numbers after a lackluster performance in the first Democratic primary debate last month.

Buttigieg, for his part, appears likely to lean into his biography even more than usual. On Monday, two major pieces were published in the Washington Post and CNN detailing the mayor’s military service in Afghanistan, one penned by the candidate himself. With his time as a U.S. Navy intelligence officer this out front before a debate, Buttigieg may be preparing to dip his toes into foreign policy—currently the favored territory of frontrunner Joe Biden, who was not in Tuesday’s debate.