That debate night moment last week symbolized the party's move to the left heading into a primary in which most candidates are trying to appeal to the progressive base. President Donald Trump immediately jumped on it to paint Democrats as extreme.
Even if Democrats win the White House and both chambers of Congress, coverage for unauthorized immigrants would mean reversing long-standing restrictions in the government's main health insurance programs and a heated political battle — more so should Republicans retain Senate control.
The issue has been considered so politically sensitive that the "Medicare for All " bills in Congress don't explicitly say they'd cover immigrants here without legal permission. Instead legislation from Sen. Bernie Sanders, I-Vt., and a House counterpart calls for covering every U.S. "resident" and delegating the nation's health to define that term.
The Senate bill has been endorsed by several of Sanders' rivals for the Democratic presidential nomination, including Sens. Cory Booker of New Jersey, Kirsten Gillibrand of New York, Kamala Harris of California and Elizabeth Warren of Massachusetts.
Debating in Miami last week, Democrats argued that all Americans would be better off if everyone in the country had medical care. They pointed out that most immigrants are working and paying taxes that support programs such as Medicare and Social Security.
"You cannot let people who are sick, no matter where they come from, no matter what their status, go uncovered," former Vice President Joe Biden said. Biden's approach calls for building on the Obama-era law he helped to pass, which now denies benefits to immigrants living in the country without permission.
It wouldn't be a freebie, argued South Bend, Indiana, Mayor Pete Buttigieg, who has talked about a buy-in plan. "They pay sales taxes, they pay property taxes directly or indirectly," Buttigieg said. "This is not about a handout. This is an insurance program."
Other Democrats say program design could lead to broader public acceptance. "If it is clear that they are paying for it, they could be getting basic care and avoid being in the emergency room at taxpayer expense," said Rep. Ro Khanna, D-Calif.
Trump all but thanked the 10 Democrats on the debate stage. "All Democrats just raised their hands for giving millions of illegal aliens unlimited healthcare," he wrote on Twitter. "How about taking care of American Citizens first!? That's the end of that race!"
A CNN poll raised a warning flag that echoed Trump's dismissive tweet: Among all Americans, 59% were opposed, while 38% were in favor. But Democrats had a different view. Roughly 6 in 10 Democratic voters for government health insurance coverage for people in the country illegally. The poll also highlighted a generational difference. Democrats under 45 supported coverage by 70% to 29% while those 45 and older were more closely divided, 55% to 41%.
For now, flagship federal health programs remain off limits to all but U.S. citizens and legal residents. That includes Medicare, Medicaid, Children's Health Insurance and the Obama-era Affordable Care Act. Congress even forbade unauthorized immigrants to buy ACA coverage with their own money.
America doesn't slam the door completely. Federally funded community health centers provide basic medical care to the uninsured without asking immigration questions. Hospital emergency rooms are required by law to treat and stabilize all patients, with government subsidizing the cost. Some states, like California, use their own funds to cover children regardless of immigration status.
Of the 10 million to 11 million immigrants in the country without legal permission, many appear to have private coverage. The Kaiser Family Foundation estimates that roughly 4 million people are uninsured because of immigration status, while the Migration Policy Institute has a higher number, nearly 6 million. Both are nonpartisan research organizations.
Opponents of covering unauthorized immigrants say it will only encourage more migration — a potential problem supporters of the idea have acknowledged. The Medicare for All bills call for measures to deter immigration for the "sole purpose" of getting free medical care.
"Adopting subsidized major health care programs for illegal aliens serves as the ultimate 'pull factor' for migrants and would exacerbate our nation's border crisis," said R.J. Hauman of the Federation for American Immigration Reform, which supports curbs on immigration.
Cost is another factor. Hauman said it would be a new "multi-billion dollar" expense for taxpayers. However, independent experts at the Kaiser Foundation and Migration Policy say there's no authoritative number because the question hasn't been rigorously researched.
Randy Capps, a senior researcher with the Migration Policy Institute, said immigrants living in the country illegally are generally a younger population, so bringing them into the private insurance system could also help with costs.
"Undocumented immigrants are disproportionately young and healthy," Capps said. "From the point of view of providing preventive and primary care to a large group of people who are younger and healthier now but might get sicker later, it makes sense."
Associated Press writer Nicholas Riccardi in Denver contributed to this report.