Since the Republican healthcare bill went from an unpopular boondoggle to an outright failure last month, Democrats have started to shift from defense to offense. The Affordable Care Act is alive, at least for now—so progressives are looking ahead to reforms they can advance if and when they get back in power.

In recent days, Democratic senators Bernie Sanders and Brian Schatz have drawn major attention for teasing elements of upcoming proposals to expand the number of Americans with insurance and the quality of care they get. These plans are part of a broader debate about what healthcare ideas the Democrats should run on in 2018 and 2020, a debate that could define the party for years.

Democrats, says Progressive Policy Institute President Will Marshall, are united by a common belief in universal healthcare coverage. But there are disagreements on how to get there.

Broadly, the healthcare visions floating around the Democratic Party fall into three camps. The first, and most centrist camp, wants to double down on the Affordable Care Act, focusing on improving its framework to increase coverage and cut costs. Only one of these tweaks—stabilizing the ACA marketplaces by guaranteeing subsidies threatened by the Trump administration—can be achieved by bipartisan means in this Congress. So though making small changes is the most modest course of action, it's still not achievable until Democrats control the government. As of now, says healthcare policy opinion researcher Robert Blendon, this position has the most traction—including among the Democratic leadership.

The most radical camp wants to scrap the ACA and create a single-payer healthcare system where the government provides insurance to everyone. Plans to build such a system by expanding Medicaid or Medicare have been around since the 1940s, and the idea has been relatively popular at various points, but no single-payer proposal has ever come close to passing. Hillary Clinton dismissed the notion as entirely impractical in the 2016 election cycle.

The final camp includes plans like Schatz's, which call for something in the middle. In his case, this means giving states the option to open Medicaid to anyone who wants it. Proponents of this approach—sometimes called a "public option"—think that government-provided insurance would be more effective than private insurance at providing for chronically underserved communities, or at least create a baseline against which private insurers would have to compete. Other plans exist in this middle space to put Medicare onto the ACA markets instead of Medicaid, expand eligibility for that program even further, or something similar. This is more moderate than going single-payer, yet more radical than sticking with the ACA framework as it stands. But Schatz and Sanders have both alluded to the possibility of using expansions like these as a stepping-stone toward a single-payer system.

If these latter two camps' plans sound a little vague, that's because they are. Mark Peterson, a 30-year veteran of healthcare policy debates, notes that politicians have in the past crafted full and detailed bills outlining single-payer or other plans. But so far no one appears to be clearly building off of them. Without details, it's hard for experts to gauge proposals' viability and easy to subject them to waves of broad, theoretical critique.

"We're at a stage where these ideas are on parallel tracks that are all running and nothing has gelled," says Kaiser Family Foundation CEO and president Drew Altman. "They're somewhere between political slogans that are being tested out and policies that are being proposed."

At this stage, Altman says, the debate isn't really about the particulars of any possible proposal—which makes sense, since no healthcare bill proposed by a Democrat will have a chance of becoming law until at least 2021. It's an abstract debate about how far down the progressive path the Democrats should position their party in the next two national elections and beyond. "These are really proxy issues for larger debates the party is going through that are completely unresolved," Altman says. "And they will probably remain unresolved right down until they pick a [presidential] candidate."

This lack of clarity hasn't stopped single-payer advocates from pushing potential candidates in the 2018 and 2020 elections to run on that ill-defined platform, insisting that it will be the future of the party. "I hear from my friends who are politicians that there's already pressure to declare, 'Are you for single-payer or are you not?'" says Marshall.

Some Democrats will buy into this call, argues Blendon, because the progressive base, which is vital in many primary elections, is gunning for something that goes beyond fixing the ACA. But though party leadership has voiced openness to a single payer or public options plan, they aren't likely to fully embrace it, at least not in this election cycle. No one's sure at this point whether a left-wing message like single-payer will consistently win primaries, says Brookings Institute healthcare expert Alice Rivlin, much less general elections.

"Political leaders are wise and understand that if you're running in, say, rural Indiana… you're in a tough competitive district, then let's let those candidates figure out the formula that's going to let them win and take back seats controlled by Republicans," says Marshall, "rather than have this a priori purity test that everybody has to pass before they go out and campaign in all these places with very different characterstics."

If candidates espousing progressive healthcare proposals win enough seats in 2018, the party may be amenable to working their ideas into its platform, or throwing more weight behind lefty candidates. But even if they do, they're more likely to opt for middle-road plans and candidates. Single-payer might be an effective rallying call in abstract, but when push comes to shove politicians and swathes of the public may get scared off by the amount of disruption and the tax increases that will be involved. That's what has torpedoed single-payer proposals in the past, and why many are skeptical this time around too.

"Single-payer is just too hard to pay for," predicts Rivlin. "The practicalities will win in the end."

"Then the middle comes back with, 'let's have something that's in-between and give people choices,'" says Blendon. The specific contours of such a middle-road plan will depend on dynamics within the party and the electorate when decisions are being made, though.

There's also the possibility that after 2018, Democrats figure they are better off just making positive tweaks to the ACA and stepping away from healthcare as a deciding issue for a while. "Do Democrats want to be consumed for another eight years by another massive and risky health proposition?" mused Marshall. "I don't think it reflects the public's top priorities, which I think are better jobs and higher wages."

"I don't see a groundswell of public support" for progressive ideas like a public option or a single payer system, he added "I think the public has got healthcare fatigue."