(CNN) - The question of the future of private health insurance revealed the starkest divide on policy among the 10 Democratic presidential candidates onstage in Miami, as the first debate night of this 2020 primary began with an early bang.
Presented with a question that cut to the core of the "Medicare for All" debate, Massachusetts Sen. Elizabeth Warren raised her hand and said she backed eliminating private plans in order to launch a new, single-payer system. She then offered a forceful argument on its behalf -- slamming the for-profit insurance industry as immoral while most of the stage served up more moderate plans that would retain a role for insurers.
Despite his absence, Vermont Sen. Bernie Sanders loomed large in the debate -- and never more so than during the health care exchange.
Medicare for All has been the clearest dividing line in a primary that has skewed progressive. The most heated debates on the stump -- and among liberals on its periphery -- have centered on whether the next Democratic president should seek to revamp President Barack Obama's landmark health care law or effectively blow it up in favor of a radical remaking of the nation's health care system.
Warren's unequivocal answer drew her still closer to Sanders' own position, further reducing the easily discernible differences in their progressive pitches. Her words drew the attention -- and some adulation -- from leftists and progressives on social media, including some dedicated Sanders supporters. Her remarks could further tighten what is shaping up to be a competitive race for the support of the party's emboldened left.
"I'm with Bernie on Medicare for All," Warren said, when asked if she would pursue as president her primary rival's plan, which would be phased in over four years, before turning the screws on the private insurers.
Adam Green of the Progressive Change Campaign Committee, longtime Warren supporters and 2020 endorsers, said that her answer "on Medicare for All gave anyone who prioritizes that issue a permission structure for clearly voting for her."
"But it also spoke to swing voters, by making the case against for-profit insurance (companies) that make money by denying their family's care," Green said. "So it really was a win-win, covering the progressive base and swing voters who will be necessary to defeat Trump."
And while Sanders was absent, awaiting Thursday's event, his chief of staff, Ari Rabin-Havt, weighed in afterward.
"Nearly every candidate onstage says health care's a human right. The question they all have to answer is how do you get there?," he said. "And Bernie Sanders' Medicare for All plan is the actual way to make health care a human right."
Of Warren's answer, specifically, Rabin-Havt said: "She co-sponsored Bernie Sanders bill in 2017 and there's no reason to think that she doesn't support Bernie Sanders' approach to health care."
Outside of the growing progressive consensus -- on the issue, if not the candidate -- there was also a robust debate over what the future of health care might look like with a Democratic president less interested in pursuing a politically risky, Medicare for All agenda.
Amy Klobuchar, a Senate colleague of Warren and Sanders, said she preferred a "public option" like what former President Obama had initially proposed. Calling that ultimately failed proposal "bold," she offered words of caution about the Sanders bill, which Klobuchar is one of only two senatorial candidates not to co-sponsor.
"I am just simply concerned about kicking half of America off of their health insurance in four years," Klobuchar said, referring to the 150 million-plus people who have private coverage through their employers. She later added that she believed every Democrat agrees on pursuing universal health care but that her preferred path is a public option, which would give Americans a choice of a government-sponsored plan alongside those offered by private insurers.
Former Texas Rep. Beto O'Rourke allowed that the goal should be "guaranteed, high-quality, universal health care as quickly and surely as possible." But when pressed on whether he would support replacing private insurance entirely, he responded, "No."
"Our plan says that if you're uninsured, we enroll you in Medicare," O'Rourke said, who favors a plan called Medicare for America. "If you're insufficiently insured, you can't afford your premiums, we enroll you in Medicare. But if you're a member of a union that negotiated for a health care plan that you like because it works for you and your family, you're able to keep it."
That prompted a direct response from de Blasio.
"Why are you defending private insurance to begin with?" the New York mayor asked, directing his question at O'Rourke. That's when former Maryland Rep. John Delaney, a vocal Sanders critic, jumped in to take the side of his one-time House colleague.
"One-hundred million Americans say they like their private health insurance, by the way," Delaney said. "I mean, I think we should be the party that keeps what's working and fixes what's broken." The crowd in Miami broke into applause.
Delaney warned that forcing hospitals to pay at Medicare's rates would put them out of business. He also offered praise for private plans offered by labor unions.
Others were less clear on where they stood. Tulsi Gabbard, the Hawaii congresswoman, restated her support for Medicare for All, but also suggested keeping private insurance -- something Sanders's bill all but eliminate -- should be something to consider. She pointed out that most countries with universal coverage still maintain a market for private insurance.
Likewise New Jersey Sen. Cory Booker did not offer a defense of keeping private insurance, although he has stated in the past he would support private insurance. In addition to co-sponsoring Sanders's bill, Booker is also a co-sponsor of multiple bills -- some of which would allow Americans to buy into Medicare or Medicaid and others that would offer a public option that would maintain a private health-insurance market.
"Health care, it's not just a human right, it should be an American right. And I believe the best way to get there is Medicare for All," Booker said.
The issue of keeping or eliminating private insurance came to the fore in January when California Sen. Kamala Harris, who will be debating on Thursday, appeared at a CNN town hall and embraced Medicare for All. Pressed by CNN's Jake Tapper about whether she supported eliminating private insurance, Harris said she would -- an answer her campaign would walk back the following day.
Warren, like Harris, had previously said she supported several paths to Medicare for All that could allow for maintaining private insurance. But her aggressive defense of the Sanders bill Wednesday showed the Massachusetts senator was firmly staking out the more left-leaning position.
She may also be encroaching on Sanders' turf and, Warren hopes, some of his voters. Her pitch Wednesday night on Medicare for All was aimed squarely at the type of anti-establishment voters looking for a populist fighter, a group the Vermont senator has courted since his previous White House bid.
"There are a lot of politicians who say, oh, it's just not possible, we just can't do it, have a lot of political reasons for this. What they're really telling you is they just won't fight for it," Warren said from her podium in the middle of the stage. "Well, health care is a basic human right, and I will fight for basic human rights."
On the far end of the stage Delaney, a long-shot candidate, offered a counter-message intended for pragmatists in the party.
"We need real solutions," he said, "not impossible promises."
CNN's Tami Luhby contributed to this story.