Read: Obamacare bars illegal immigrants—and sticks hospitals with the bill

“If we are saying that we can put them into the pools and they can buy on the exchange, I don’t think voters are going to flip out on that because there is no subsidy,” says Matt Bennett, the executive vice president for public affairs at Third Way, a leading organization of Democratic centrists. “But I think beyond that gets pretty dicey.”

This debate affects millions of people. The Kaiser Family Foundation, using census data, has estimated that 47 percent of the country’s roughly 11 million undocumented immigrants are uninsured, compared with one-fourth of legally present immigrants and about one-tenth of American citizens. Similarly, the Urban Institute places the number of uninsured undocumented immigrants at nearly 4.9 million, or about one-sixth of the total population of uninsured people in America.

The case for expanding their health-care access rests on financial, public-health, and moral arguments. Supporters contend that it’s cheaper to provide access to medical care up front, rather than deal with health crises in emergency rooms; that allowing the undocumented to go untreated increases health risks for legal residents who come in contact with them; and that it is unjust to let people face health threats without care, regardless of their status. As Biden put it in a recent interview with CNN, “How do you say, ‘You’re undocumented. I’m going to let you die, man’? What are you going to do?” The counterargument, meanwhile, is that it’s unfair to ask taxpayers to subsidize their care, and that covering the undocumented will act as a “magnet” to incentivize more immigration.

Emergency rooms must provide aid to all who need it. But polls have consistently found that most Americans resist offering public benefits to the undocumented beyond that. In a recent CNN survey, Americans by a solid 3–2 margin said that “health insurance provided by the government” should not be available to immigrants here illegally. The idea faced resistance across a wide array of constituencies, including several that Democrats rely on: Just over half of college-educated white voters, half of young adults ages 18 to 34, and more than two-fifths of nonwhites said they opposed providing coverage for the undocumented. At the same time, three-fifths of voters who identified as Democrats or lean Democratic said they support the idea.

This mixed result leaves the 2020 candidates balancing competing political and policy considerations as they confront the question. In the process, they have reopened a debate that extends back to the consideration of the ACA during former President Barack Obama’s first year in office.

The original version of the ACA, passed by the Democratic-controlled House in November 2009, allowed undocumented immigrants to purchase insurance on the law’s exchanges with their own money. But it denied them eligibility for the subsidies the law established to help the uninsured afford such coverage, and it maintained their exclusion from Medicaid, which the ACA expanded to cover more of the working poor.