Up until recently, most of the Democratic hopefuls for 2020 have gotten away with being vague about what they mean by Medicare for all. But keeping up the ambiguity is getting harder because journalists keep asking one very particular question: Do they, or do they not, want to eliminate private health insurance?

Some of answers have been more detailed than others. Last week, California Sen. Kamala Harris told a CNN town hall that she’d definitely prefer to do away with private coverage—“let’s get rid of all that,” she said—but also suggested that it wouldn’t be at the top of her to-do list as president. Massachusetts Sen. Elizabeth Warren, on the other hand, danced awkwardly around the question, telling Bloomberg her goal was “affordable health care for every American,” whatever that means. Ohio Sen. Sherrod Brown offered a clear no; he suggested to a group in Iowa that Medicare for all wasn’t “practical” and said he wanted to let Americans buy into the program at 55 instead. Cory Booker was also a nay: “Even countries that have vast access to publicly offered health care still have private health care, so no.”

Part of the reason this issue has suddenly flared is that, to the activist left, “Medicare for all” really means one thing: a single-payer health care system where all Americans receive coverage through one comprehensive government insurance program. That is essentially the plan Vermont Sen. Bernie Sanders, another likely 2020 candidate, campaigned on in 2016. It’s what the Medicare for all bill he introduced in 2017 is designed to do.

Many of Sanders’ potential opponents co-sponsored his legislation, including Harris, Warren, Booker, and New York Sen. Kirsten Gillibrand. And while some of them may have done so merely as a vague philosophical gesture in favor of expanding government insurance, or just to make nice with Sanders and his fans, it’s fair to ask them now whether they support the bill’s actual contents. But recent polling has made answering that question seem politically perilous. While the phrase “Medicare for all” is popular with just about everyone, the Kaiser Family Foundation has found that more than half of Americans believe it refers to a system where they would be allowed to keep the health plan they currently get from their employer. When people are told that private coverage would be banned, support drops to just 37 percent.

Technically, Sanders’ bill does not eliminate private insurance outright. Instead, it bars companies from selling coverage that “duplicates” any benefit provided by the new Medicare program. Carriers like Aetna or Cigna would still be allowed to offer supplemental policies covering services the government won’t pay for. But practically speaking, employer-based coverage as Americans know it today would disappear. Even if you like your plan, you would not be able to keep it.

So candidates are faced with two seemingly unpalatable choices: Oppose single payer, and they risk alienating the left; support it, and they risk staking out a position that might be unpopular in the general election.

Worse yet, this whole debate has a slight air of political theater. Single payer has a quark-size chance of passing the Senate. Doing so would require finding 60 votes to support it, or eliminating the filibuster and finding 50 votes to entirely scrap the existing U.S. health insurance system. Even Sanders himself seems to be aware that single-payer may not really be in the cards given that he’s endorsed some more moderate alternatives, such as a bill to let Americans buy into Medicaid on Obamacare’s exchanges.

So looked at one way, having a big public debate about the merits of single payer might seem both dangerous for Democrat, and pointless.

But in the end, I think the argument is healthy.

First, it’s only fair to members of the left, which deserves a clear choice between candidates who might actually champion single payer against long odds and those who won’t. Up until now, Democrats have sought to blur those differences. Duping ideologically committed primary voters into thinking you’re on their side, then tacking to the center during the general might be OK short-term politics, but it’s also the kind of thing that breeds cynicism and distrust of politicians.

Perhaps more importantly, having this awkward conversation now will give the party a chance to figure out what Medicare for all should actually mean. Bernie Sanders convinced many young and progressive voters that America ought to adopt something that looks like a version of Canada’s health care model, but more generous. (Public insurance there typically excludes things like prescription drugs, dental, and vision care, all of which Berniecare would cover; Canadians often rely on private insurance for those benefits.) But Sanders’ vision of a medical system where almost all services are paid for by the government with zero out-of-pocket expenses for consumers would ultimately be unique. In other developed countries, universal health care schemes usually involves some cost-sharing schemes; it’s fair for voters to be skeptical about whether Berniecare would work out as promised or be sustainable.

As Booker has pointed out, there are other ways to do universal health coverage where private insurance plays a greater role. Australia and the U.K., for instance, both provide their residents with government health coverage (in Australia, it’s literally called Medicare). But individuals are permitted, and in Australia’s case even encouraged, to buy private policies that can help them get faster access to care or more choice of doctors and hospitals.

Different approaches have different pluses and minuses. Canada’s model is egalitarian and straightforward, but people can end up waiting a long time to see a doctor. Private coverage creates a two-tier system in Australia and the U.K., but it also gives people who really, really don’t want to wait for that hip replacement surgery a way to avoid the line at a public hospital. It’s a political pressure release valve.

It’s worth it for Democrats to debate, in an upfront and honest way, whether the party’s end goal should be to funnel every American into a single and hopefully generous insurance system, or something with a bit more flexibility where the private sector has a bigger role. Even if the goal really is single payer, or close to it, there’s a question of how to get there. Do you outright ban private insurance? Or do you design a plan, like the one proposed by the Center for American Progress, that would let companies choose between buying their workers private coverage or a Medicare plan, knowing that the vast majority of them will probably transition to the latter?

Primaries are a good time to suss out these kinds of questions—they’re one of the few moments Americans really tune in for policy debates, before legislation is actually being introduced on the Senate floor. In 2016, Bernie convinced a lot of the country that Medicare for all sounded like a good idea. Now would be a good time to figure out what that idea should actually be.