Two years ago, Sen. Bernie Sanders introduced a “Medicare for All” bill that would move the U.S. toward a single-payer healthcare system. He didn’t get a single co-sponsor.

On Wednesday, the Vermont independent will introduce his latest version of the bill. Ten of his colleagues—about one-fourth of Democratic senators—have already signed on.

That includes four senators widely expected to run for president in 2020: Elizabeth Warren, Cory Booker, Kamala Harris and Kirsten Gillibrand.

“The American people understand that now is the time for us to do what every other major country on earth does and guarantee healthcare to all people,” Sanders told TIME in a hallway of the Capitol Building on Tuesday.

But Sanders’ has been preaching the single-payer gospel for years. The question is why the choir behind him has grown.

One major reason is that President Obama is no longer in office. As the putative head of the party and the namesake of Obamacare, his Administration kept the focus on implementing and defending the Affordable Care Act.

The 2016 election also led to a paradigm shift for many Democrats, who felt that Hillary Clinton’s campaign offered too many smaller initiatives, especially when contrasted with Donald Trump’s all-caps promises to build a wall.

“Do we need to be a little bit edgier and bolder in our policy prescriptions in terms of how we talk about and address those issues? I think people do take that away as a lesson from 2016,” one senior aide to Democratic leadership said.

Voters have also warmed up to the idea, especially over the last year. Sixty percent of Americans now believe the federal government is obligated to ensure healthcare coverage for all, according to a Pew Research Center poll published in June.

Jennifer Victor, a political scientist at George Mason University, says the increased support for Medicare for All is a sign of the split between the Clinton and Sanders wings of the party.

“We’re now seeing an intra-party struggle over what the spirit of the party is,” she said. “The support that Sanders has gotten is a sign that the progressive wing of the Democratic Party is quite a bit stronger and more vocal than it has been in the past.”

More pragmatic Democrats, especially among party leadership, have made it clear that the priority should be sustaining and improving Obamacare, rather than pursuing a more ambitious overhaul. That’s mostly a defensive strategy: Republicans, led by Sens. Lindsey Graham and Bill Cassidy, are eyeing a final long-shot attempt at repealing the Affordable Care Act this month.

(Republicans remain just as skeptical of Medicare for All. Republican Sen. John Barrasso from Wyoming described it as a “complete government takeover.”)

“Clearly there have always been, and still are, people in the Democratic Party who would like to see a public option,” House Minority Whip Steny Hoyer said on Tuesday. “As a practical matter, we ought not to divert our attention from the immediate objective, which is making sure the ACA remains the law and that we fix it so it works for as many people as productively, efficiently, and cost-effectively as possible.”

Speaking to reporters on Tuesday afternoon, Senate Minority Leader Chuck Schumer declined to give his specific thoughts on Sanders’ proposal.

“Democrats believe that healthcare is a right for all,” Schumer said. “And there are many bills out there. Many good ones.”

The strategy favored by Democratic leadership is a bipartisan effort spearheaded by Republican Sen. Lamar Alexander and Democratic Sen. Patty Murray, which would continue to subsidize insurance companies that reduce out-of-pocket costs for low-income Americans.

It is a far cry from the universality of Sanders’ single-payer system. But the growing chorus of Democratic voices backing the Sanders plan suggests that the issue isn’t going away—though in terms of enacting policy, it will almost certainly remain a mostly hypothetical fight until Democrats regain power.

As one Senate Democratic aide put it: “We can’t have a serious conversation about a Democratic bill that goes beyond [the Affordable Care Act] until we have the power to enact it—until we have the White House.”

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