It’s one of the major litmus tests for 2020 candidates for the Democratic nomination for president: Do you support Medicare for All?

But it turns out it’s not an easy yes or no question. While the idea of it has become very popular, with 70 percent of Americans saying they're in support, according to a recent Reuters-Ipsos poll, those numbers shift when pollsters get more specific.

When asked if they would support Medicare for All if they had to pay higher taxes or if private insurance companies were eliminated, support among Americans drops sharply to just 37 percent in both instances, according to a Kaiser Family Foundation poll in January.

So while Medicare for All seems like all the rage, particularly among Democrats running for president, what it actually means depends on who, and sometimes when, you ask. On the one hand are Democrats who support Sen. Bernie Sanders’ version of Medicare for All, which replaces private health insurance with a state-run single-payer system. On the other are people who support some kind of public insurance option as part of a menu that includes private insurance.

But the debate splinters even further. On Wednesday, moderate Democrats introduced a bill, nicknamed “Medicare for More,” that’s significantly less sweeping than Bernie’s plan. The bill allows people between the ages of 50 and 64 to buy into Medicare, a plan that more closely mirrors the ideals of 2020’s center candidates.

Here’s where the candidates stand, roughly on a scale of most to least extreme:

Medicare for All: The full Bernie

Right now, there are three 2020 contenders who are explicitly on board with that: Sen. Sanders, Sen. Kamala Harris of California, and Sen. Kirsten Gillibrand of New York.

This scenario bans companies from selling health insurance that competes with what’s being provided by the government. Because the benefits offered in the bill designed by Sanders are sweeping, it would virtually eliminate private insurance as we know it, or limit it to elective procedures such as plastic surgery.

Medicare for All: We’re keeping it vague

Some supporters of Medicare for All, such as Massachusetts Sen. Elizabeth Warren, (though she is a co-sponsor on Bernie’s bill) and Texas’ Julian Castro, haven’t been clear on what their support really means. Warren has willfully ignored the private-insurance question and has said there are “obviously multiple ways” to get to universal healthcare.

Elizabeth Warren

Medicare for All: As an option

Though he is also a co-sponsor of Bernie’s bill, New Jersey Sen. Cory Booker is the most prominent Democrat to embrace this approach, which would allow Americans to choose public insurance or keep their private insurance. Critics say it’s not realistic because healthy people will pick private insurance, leaving Medicare as the place to go for those who are already sick or in poor health. Beto O’Rourke, who has not declared he's running, previously expressed support for Medicare for All but later backtracked and said he supports a “public option” for healthcare.

Cory Booker

Medicare for All: For older people

Others such as Sen. Sherrod Brown of Ohio and Sen. Amy Klobuchar of Minnesota oppose Bernie’s Medicare for All bill and favor more-moderate reforms, such as “Medicare at 50,” which would allow people to get Medicare once they reach a certain age. Both Klobuchar and Brown co-sponsored the legislation introduced Wednesday to lower the Medicare-eligibility age from 65. Both senators have expressed support for a public insurance option.

Amy Klobuchar

“I want universal coverage, and I believe we can get there,” Brown told VICE News in a statement. “I also want to make people’s lives better right now. That’s why I support opening Medicare up to people in their 50s to buy in. That will do two things: make life better for millions of people right now and get us closer to the goal of getting everyone covered.”

Medicare for who knows?

Former Vice President Joe Biden hasn’t declared if he supports the idea, but he was also an architect of Obamacare, which imposed a structure of regulated private exchanges over the private healthcare system and imposed tax penalties on people who did not enroll in health-insurance programs. It also allowed states to decide whether to expand Medicaid to make it available for more people.