Health care has sucked up a lot of oxygen during of the Democratic debates. And although it’s easy to lose sight of the broader stakes when the candidates are debating the finer points of the health care system, its fate is often a deeply personal and pressing topic for voters, especially when it comes to costs and coverage. So understanding the fears and concerns that have driven health care to the top of voters’ agendas can also help illuminate one of the biggest fault lines that’s emerged in the primary so far — whether it’s a good idea to eliminate private health insurance in favor of a single-payer, government-run system.

The Democratic candidates have basically split into two camps on this question. A more progressive group, led by Sens. Bernie Sanders and Elizabeth Warren, supports a “Medicare for All” system, where a single-payer, government-run plan would eventually replace the current system that includes private insurance. Then there’s the more moderate group, including former Vice President Joe Biden and South Bend, Indiana, Mayor Pete Buttigieg, who advocates “Medicare for all who want it” or a public option, that would build on the Affordable Care Act by adding a buy-in option for a government-run plan while still maintaining a role for private insurance.

Both options are quite popular with Democratic primary voters, too — although polling has shown that the public option seems to have an edge. According to a Kaiser Family Foundation poll conducted in late November, 77 percent of Democrats support a national Medicare for All plan. But an even larger majority (88 percent) support a public option. Another KFF poll conducted in September found that when asked to choose, a majority (55 percent) prefer a candidate who would build on the ACA, while 40 percent favor a candidate who would replace the ACA with Medicare for All.

Democrats’ rising dissatisfaction with the health care system can help explain why the issue is getting so much traction in the primary. According to a Gallup poll released earlier this year, 84 percent of Democrats say the health care system is in a state of crisis or has major problems — an increase of more than 20 percentage points since 2016. Ashley Kirzinger, associate director for public opinion and survey research at KFF, said that this is likely due in part to the increasing prominence of health care in the political atmosphere after Sanders’s run for president in 2016 and President Trump’s attempts to kill or undermine the ACA. But she added that Democrats are also responding to a real increase in out-of-pocket health care costs, fueled by rising premiums and deductibles.

However, despite frustrations with costs, most Democrats still hold positive views of their own insurance coverage and the quality of the care they receive. That tension helps explain why getting rid of private insurance has emerged as a key fault line — even in a campaign hyper-focused on improving the health care system.

Democrats are generally much more likely than Republicans to support government intervention in the health care system. So it’s not a surprise to see health care taking a central role in the primary. But the recent prominence of Medicare for All in the national conversation may have actually widened the gap between the parties. Polling by the Pew Research Center shows that both Democrats and Republicans saw an uptick in support for the idea that the government has a responsibility to provide health care coverage for all Americans after the 2016 election — but the share of Republicans who held this view declined sharply again last year.

All of this signals that a full-throated embrace of Medicare for All could be a liability for a Democratic candidate in the general election. Robert Blendon, a professor at Harvard University who studies public opinion on health care, pointed out that even today’s Medicare system includes an option to buy into a private plan, which about one-third of Medicare recipients choose. “I just don’t think the candidates for Medicare for All did their homework,” Blendon said. “Even Medicare isn’t a single-payer plan. Many Americans just like the idea of having a choice.”

But supporters of the different plans aren’t necessarily on the same page about how broken the health care system really is. A New York Times/Commonwealth Fund/Harvard T.H. Chan School poll conducted in October, which Blendon helped design, found that people who prefer a Medicare for All-style single-payer plan over a more incremental alternative also have a much more negative view of the health care system generally. Fifty-six percent of supporters of a Medicare for All plan said they were dissatisfied with the cost of their own health care, compared with 44 percent of people who prefer a plan that builds on the ACA. This probably helps explain why some Democrats are now throwing their weight behind a plan as radical as Medicare for All — for them, its disruptiveness is probably a feature, not a bug.

Nevertheless, sizable majorities of all Americans — regardless of which plan they support — say they’re satisfied with their current health insurance and the care they personally receive. The New York Times poll found that 79 percent of Medicare for All supporters who are insured say they’re satisfied with their own coverage. And according a KFF poll conducted July, 86 percent of Americans with insurance rate their personal coverage positively. That’s in line with past polling which has found that Americans tend to have a much rosier view of the health care they personally receive than the health care system in general or the cost of health care. And their general skepticism of government may make them even more inclined to cast a skeptical eye on a single government-run health care plan. “People might not love the insurance companies, but do they really trust Congress more?” Blendon said. “Some people want another option, in case they don’t like the government’s plan.”

There are still some ways for candidates like Sanders and Warren to try to alleviate some of voters’ concerns about Medicare for All, Kirzinger said. According to the November KFF poll, for instance, a majority (54 percent) of Americans said they’d support a government-run plan that eliminated private insurance if it still allowed people to choose their doctors, hospitals and other providers.

But Blendon said there’s another risk in talking mostly about big changes to the system — it becomes harder to explain how these shifts will bring down the price of insulin or reduce emergency room bills. And that’s a problem if voters are really preoccupied with costs. “When you’re talking about a dramatic overhaul of the system, you’ve got to talk about how you’re going to cover everyone, and the financing, and the extent of the benefits,” he said. “The amount of change being proposed could be scaring people.” And that, in turn, makes it harder to focus voters on the impact that Medicare for All could have on their own wallets.