The Democrats’ 2020 primary has kicked off with a confusing and confused debate about the details of Medicare-for-all — one that shows just how much complexity lurks behind a seemingly simple slogan.

Sen. Kamala Harris (D-CA) started things, telling CNN’s Jake Tapper that she’d “eliminate all of that,” where “that” referred to private insurance. Within a few hours, her staff was softening the statement, telling reporters that while pursuing single-payer health care was Harris’s goal, she had also signed on to more incremental bills. (“I want a burrito,” tweeted Harris’s communications director, in an impish clarification. “I’d accept tacos in the meantime, but I want a burrito.”)

Sen. Cory Booker (D-NJ) took another tack after announcing his candidacy. Asked whether he would “do away with private health care,” Booker replied, “even countries that have vast access to publicly offered health care still have private health care, so no.”

Within a few hours, Booker was besieged by angry tweets from liberals reminding him that he was a co-sponsor of Sen. Bernie Sanders’s (I-VT) Medicare for All bill and that the bill abolishes private insurance. (It actually doesn’t — more on that in a moment.) So, they said, he’d just proven himself a fake progressive and a real hypocrite.

Sen. Elizabeth Warren (D-MA) quickly surveyed the wreckage and decided to sidestep the whole mess. “We know where we’re aiming, and that is every American has health care at a price they can afford,” she told Bloomberg. “There are multiple bills on the floor in the United States Senate. I’ve signed on to Medicare for all. I’ve signed on to another one that gives an option for buying into Medicaid.”

Sanders, who deserves credit for making Medicare-for-all the defining policy of the 2020 Democratic primary, took the opportunity to tout his bill. “I look at polling and 70 percent of the people support Medicare for All,” he told the New York Times. “I think I’d be pretty dumb not to develop policies that capture what the American people want.”

Meanwhile, Sen. Sherrod Brown (D-OH), another likely 2020 candidate, decided to stake more moderate ground. “I know most of the Democratic primary candidates are all talking about Medicare-for-All,” he told the Clear Lake Chamber Of Commerce in Iowa. “I think instead we should do Medicare at 55.” Brown, one of the Senate’s most liberal members, framed his position as simple pragmatism. “I’m going to talk about what’s practical and what we can make happen,” he continued. “And if that makes me different from the other candidates, so be it.”

Behind this debate is the fact that Democrats have embraced a politically powerful, but intentionally confusing, slogan to describe their health care goals. “Medicare-for-all” doesn’t mean what it sounds like it means. So what it does mean, or should mean, has become a defining debate within the party.

What does the “Medicare” in Medicare-for-all mean?

In the Democratic imagination, Medicare is a generous single-payer insurance system that can be extended to cover the entire country.

In reality, Medicare is a peculiar health insurance plan specifically designed for seniors and mottled by decades of political tussle. It doesn’t cover a host of conditions — like, say, pregnancy — that younger people face. It doesn’t cover vision or dental. It includes significant copays and no limit on out-of-pocket spending, which is why three-quarters of enrollees use supplemental insurance to help defray costs.

Medicare also makes substantial use of private insurance. All prescription drug coverage is provided by private insurers through Medicare’s Part D program, and about 34 percent of Medicare beneficiaries are enrolled in private Medicare Advantage plans instead of traditional Medicare.

Literally none of the plans being proposed expands Medicare insurance to all Americans, and for good reason. If Medicare-for-all actually meant everyone gets Medicare, the insurance itself wouldn’t cover what young people need covered, and quite a bit of the insurance would be private.

What a lot of people seem to mean by Medicare-for-all is Sanders’s Medicare for All bill. As Sarah Kliff’s excellent explainer details, Sanders’s legislation builds a much more generous system under the Medicare banner and, along the way, bans duplicative private insurance and sunsets the current Medicaid and Medicare programs.

It’s not quite true to say Sanders’s plan abolishes private insurance entirely — you could still buy non-duplicative private insurance — but it would mean that the roughly 180 million Americans who have private insurance would see their plans canceled.

Sanders’s bill boasts Booker, Kirsten Gillibrand, Harris, Jeff Merkley, and Warren as co-sponsors — after the 2016 election, few 2020 hopefuls wanted to let Sanders outflank them on health care — but it’s far from the consensus vision, in part because Sanders’s maximalist approach to Medicare-for-all polls poorly.

What does the “all” in Medicare-for-all mean?

People don’t like health insurers in general, but they tend to like their own health insurance. Sixty-one percent of insured Americans under age 65 say their insurance plan is an “excellent” or “good” value. Perhaps that’s why canceling people’s private plans takes Medicare-for-all from majority support (+14 favorable) to majority opposition (-21 unfavorable). Raising taxes and ending the current Medicare program does even more damage.

Sanders’s plan abolishes most private insurance, raises taxes, and replaces the current Medicare program. Moreover, it’s at least theoretically possible that his legislation, which cuts payment rates to medical providers even as it gives every American free access to all health care services, could lead to supply constraints, which are the most dangerous attack you can levy against the idea.

I wouldn’t take any polling to be prophetic, and Sanders has proven himself a uniquely effective health care messenger. Perhaps his plan would prove more robust to counterarguments with him on the trail defending it. But disrupting existing health care arrangements has been politically disastrous for everyone who has tried it.

The most-aired ad of the 2008 presidential campaign was Barack Obama’s attack on John McCain’s plan to tax employer-provided insurance, and the most-aired ads during the 2010 midterms featured Republicans flaying Democrats for cutting Medicare benefits as part of the Affordable Care Act. The American people are very risk-averse when it comes to their health care.

For that reason, other Democrats and liberal organizations have developed Medicare-for-all plans that allow people to opt in to the new Medicare program, rather than being forced onto it, and that keep total costs down.

Reps. Rosa DeLauro (D-CT) and Jan Schakowsky (D-IL), for instance, just released their Medicare for America bill, which enrolls the uninsured, along with everyone on Obamacare and Medicaid, in an expanded Medicare plan and then lets individuals and employers buy into it if they choose, with sliding-scale subsidies based on income. Yale’s Jacob Hacker, who helped craft the legislation, explained the thinking to Vox:

Health care plans have foundered again and again on the shoals of figuring out where to come up with the money. To me, this is in some ways the biggest argument for a Medicare expansion that isn’t single-payer. Where do you come up with the money if you try to essentially socialize the costs of the most costly medical system in the world? There’s a lot of money going through the employment-based system and other pathways that would suddenly go on the federal ledger. Bernie Sanders’s own team said their plan would cost about 9 to 10 percent of GDP. I’ve pointed out that the tax increase to fund World War II was about 5 percent. That’s a big number. They’re right that you’re just switching private premiums over into public taxes. But I’m incredulous about the idea that you could actually implement that kind of new tax financing as quickly as would be needed to have a universal Medicare system.

Other ideas are even more incremental. Sens. Chris Murphy (D-CT) and Jeff Merkley’s (D-OR) Choose Medicare Act would basically add an expanded Medicare option to the Obamacare exchanges, and give employers the option of buying into it as well.

Every one of these plans defines the “all” in Medicare-for-all differently. Sanders’s plan says everyone gets Medicare, whether or not they want it. DeLauro and Schakowsky’s plan says that anyone can get Medicare but those with private insurance can keep what they have if they prefer it. Murphy and Merkley’s bill makes it possible for anyone to buy Medicare, so long as they can afford it.

The incrementalists (a strange word to use for plans that are still incredibly ambitious, but bear with me) argue that their proposals are safer “glide paths” to everyone being on Medicare.

The argument goes like this: Medicare’s size lets it negotiate better prices with doctors and hospitals, leading to discounts of about 20 percent over private insurance. If Medicare is cheaper and better than private insurance, then everyone will eventually switch over. What’s the purpose of forcing people onto the program and risking a backlash that could annihilate the entire project? After all, President Obama was raked over the coals for canceling around 3 million plans that were so crummy they didn’t meet the Affordable Care Act’s relatively forgiving standards; is canceling orders of magnitude more insurance plans, and far better ones, really the lesson to take from that debacle?

The counterargument is that hospitals and doctors may decide they don’t want an all-Medicare world, and they could stop taking Medicare in an effort to encourage individuals and employers to keep buying the private insurance plans that pay them higher rates. A world in which there are no private insurance plans makes that basically impossible.

The counter-counterargument is that if doctors and hospitals so fear a world where all insurance is paying Medicare rates, they would kill the plan before it ever passed, or they would force any plan that did pass to pay higher rates. Politicians are far less trusted than medical providers, and it’s unlikely any plan could overcome the entire medical industry’s objections.

Needless to say, I’m not going to settle that argument here, and I’m not even certain who has the better end of it. But it goes to show how much of the Medicare-for-all debate is actually about your theory of politics, not just your theory of policy.

The political conservatism of Medicare-for-all

The Medicare-for-all brand is appealing precisely because it’s nonthreatening. People are risk-averse when it comes to their health insurance. They want something they know will work.

Medicare works, and Americans know it. That’s a political boon for Democrats. But it carries an implicit threat: If whatever ends up being Democrats’ Medicare-for-all bill feels risky to people, the same forces buoying the idea’s poll numbers now will sink the policy later. As one concrete example, it’s very hard for me to imagine Democrats taking Medicare Advantage away from seniors under the guise of expanding Medicare. If your bill is based on the idea that people love the current Medicare program, taking away something that people love about it will feel like a profound betrayal.

There can be a tendency, when judging presidential candidates, to let ambition act as a signal of commitment. Under that view, if Harris wants to abolish all private insurance, then she’s more committed to Medicare-for-all than Booker, and both of them are more committed than Brown, who just wants to expand the program to 55-year-olds.

But that’s a flawed way to look at policymaking. The point here is expanding better coverage to more people, so the question has to expand to include political strategy. A Medicare plan that passes into law and successfully extends coverage to 40 million people gets the country a lot closer to Medicare-for-all than a plan that envisions expanding Medicare to everyone but fails in Congress and costs Democrats the House in 2022.

I don’t think DeLauro and Schakowsky are less committed to expanding Medicare than Sanders or Harris. Instead, I think they believe that Sanders’s approach could trigger a backlash that discredits the whole project, and their bill is likelier to pass. Whether that’s true is the real debate Democrats need to have.

Nor is this only about what’s inside the plan. Process matters, too. Literally zero of these plans will pass so long as they’re held to a 60-vote threshold in the Senate. Absent a plan to get rid of the filibuster, or absent a bill that can fit entirely inside the budget reconciliation process, all of this is moot. In that world, Brown’s plan to open Medicare to 55-to-64 set is probably the best you can do.

The Democratic Party has become much more ambitious in its policy ideas in recent years, and I think it’s a change for the better. But even so, the history of health care reform is mostly a history of failure and backlash. That’s because America’s political institutions make big bills hard to pass, because moneyed interests fight like hell against its passage, and because people don’t trust the government to mess with their health care. How the various Democrats running for president propose to navigate or defuse those threats should be integral to this debate.