When he ran for president last year, Bernie Sanders picked up basically zero support from the Democratic establishment. Only one fellow Senator endorsed him, and even his fellow Senator from Vermont endorsed Hillary Clinton.

The Bernie Sanders single-payer health care plan, released on Wednesday, is a totally different story. First, Sen. Kamala Harris (D-CA) announced her plans to co-sponsor it; then Elizabeth Warren (D-MA) joined in. Then Cory Booker (D-NJ), Sheldon Whitehouse (D-RI), Ed Markey (D-MA), Brian Schatz (D-HI), and Jeff Merkley (D-OR) joined in. Kirsten Gillibrand (D-NY) will reportedly co-sponsor it as well, and Pat Leahy (D-VT), who bucked his colleague Sanders in last year’s primary, is reportedly a supporter too.

Warren, Sanders, Harris, Booker, and Gillibrand are arguably the most famous and most-admired Democratic senators in the country among the party’s base; the betting markets give a 63 percent chance that one of them will be the 2020 nominee for president.

The rest of the party is getting on board with single-payer — or “Medicare for all,” where the federal government would provide health insurance for every American financed through taxes — as well. 117 House Democrats (over 60 percent of the caucus) have co-sponsored HR 676, the Expanded & Improved Medicare For All Act offered every Congress by Rep. John Conyers (D-MI).

This is what an emerging party consensus looks like. Over time, some issues become so widely accepted within a party as to be a de facto requirement for anyone aspiring to lead it. No Democrat would run for president, or even for House or Senate minority leader, without supporting the DREAM Act. No Republican would try for a leadership position without supporting repeal of the estate tax.

And the way things are going, soon no Democratic leader will be able to oppose single-payer.

The dynamics making Democratic leaders endorse single-payer

This shift has occurred with astonishing speed. Even the left-most mainstream candidate in 2008, John Edwards, didn’t dare propose single-payer, instead backing an individual mandate, insurance exchanges with subsidies, and a public option (presaging the Affordable Care Act, at least as the Obama administration wanted it to be). Al Gore and John Kerry didn’t even pretend their health plans would lead to universal coverage. A few stalwarts in Congress, like Conyers or former Rep. John Dingell (D-MI), kept the flame alive, but in the mainstream of the Democratic party, the idea was dead.

And there are still holdouts to the new pro-single-payer consensus, for sure. Moderate Govs. Terry McAuliffe (D-VA), Steve Bullock (D-MT), and Andrew Cuomo (D-NY) have all hinted at presidential bids, and none have endorsed single-payer. Nor has Joe Biden, who would be 78 on Inauguration Day but is nonetheless putting out feelers for what would be his third run for president.

But if they want to win, the moderates are going to face the exact same pressures that have led Harris and Warren to embrace Medicare-for-all. Bernie Sanders came shockingly close to winning the 2016 primary with almost zero institutional support from the Democratic party, and he fell short in large part because of his failure to appeal to African-American primary voters, who despite preferring Hillary Clinton are more likely than white Democrats to support single-payer.

That tells prospective national candidates some important things about the primary electorate they’re trying to woo. First, it has a huge stock of voters who flocked to Sanders, a candidate who made Medicare-for-all a cornerstone of his campaign. Second, winning those voters while making more inroads among black voters is almost certainly enough to win the primary, and a populist economic message at the very least won’t hurt attempts to woo black voters.

Put it all together, and the best path to victory in the primary starts to look like mimicking Sanders on policy, and certainly on health care policy. What’s more, if Biden or Cuomo were to run and oppose single-payer, they’d be hit hard by all their opponents for being holdouts offering half measures rather than promising universal health care. By contrast, if they just got on board with single-payer, it would be more or less costless in the primary.

There’s more to elections than primaries, of course, and the crushing defeat that single-payer received when it was on the ballot in Colorado last year suggests that massive payroll tax increases of the kind that the Conyers bill and (from early indications) the Sanders bill would entail are not exactly popular with a general election audience.

But that might also be a fixable problem. Universal health care as a concept polls pretty well with the general public, and it’s possible to design a single-payer or de facto single-payer plan that doesn’t require massive tax increases. And while a victorious Democratic president who supports single-payer would have a hard time passing it, they’d have a hard time passing anything significant on health care. There’s little cost in going big.

This is a significant change. And the success of the Sanders primary campaign, along with his subsequent decision to parlay that organizing into an effort to move his colleagues to the left, deserves a lot of credit in effecting it. While he lost the nomination, Sanders appears to have succeeded in significantly shifting the Democratic consensus on one of the party’s bread-and-butter issues.