The seismic shift in support for Sen. Bernie Sanders’ plan to transform the U.S. health care system into a single-payer program indicates the reach the Vermont independent has within the Democratic Party.

At the same time that his onetime presidential foe Hillary Clinton is reminding people of the party’s devastating loss last fall, Sanders is trying to define its future. His bill to enroll every American in Medicare drew 16 co-sponsors, 16 more than when he first introduced similar legislation in 2013.

It has garnered support from possible 2020 Democratic presidential hopefuls — Sens. Cory Booker of New Jersey, Kamala Harris of California, Elizabeth Warren of Massachusetts and Kirsten Gillibrand of New York — as well as Sen. Tammy Baldwin of Wisconsin, an incumbent up for re-election next year in a state narrowly won by President Donald Trump.

It also provided a welcome talking point for Republicans who have long railed against government-run health care. Several GOP senators used Sanders’ legislation as a tool to warn voters of what could come if Republicans are unable to overhaul the health care system.

‘A political crisis’

During a bill introduction Wednesday that felt more like a campaign rally than the standard press conference, Sanders — flanked by co-sponsors — stuck to his standard script of bashing Republicans and special interest groups for doing nothing to address rising health care costs.

“The crisis we are discussing is not really about health care,” he told a crowded room of activists and supporters. “The crisis we are discussing today is a political crisis which speaks to the incredible power of the insurance companies, the drug companies and all those who make billions of dollars off of the current system.”

Watch: Sanders Unveils Medicare-For-All Bill

The politics of “Medicare for all” are divisive. And aside from a short comment about raising taxes across the board, Sanders has yet to outline a clear way to pay for such a system.

There is a divide within the Democratic Party on how to define such a system, and many Senate Democrats have yet to voice their support for Sanders’ plan, including vulnerable incumbents up for re-election such as Sen. Joe Manchin III of West Virginia.

Despite those differences, however, the expanding coalition of Democrats who now back such a proposal is a display of just how Sanders, who gave Clinton a serious challenge for the presidential nomination, continues to influence the national party.

“Sen. Sanders’ presidential campaign was a phenomenon that very few people saw coming. It uncovered a groundswell of progressive activation that the party now rightly wants to tap into as we head into 2018 and 2020,” Connecticut Democratic Sen. Christopher S. Murphy said. “I think that Democrats now feel a little freer to imagine some even bigger and bolder ideas.”

Asked whether the growing support for his legislation is indicative of his influence, Sanders hedged.

“Right now, we are focusing on what the bill is about,” he said. “We’ll talk about the politics of it later.”

A national message?

Several other Democratic senators supported the national party embracing more bold ideas — like Medicare for all — in the fallout from the 2016 election and tied that movement directly to the success of Sanders’ campaign.

“It’s an idea whose time has come. There’s a clear recognition that universal coverage has to be the goal,” Democratic Sen. Richard Blumenthal of Connecticut said. “These principles are now in the public mind, front and center, and that is due, in part, to the prominence that Bernie Sanders gave to them during the campaign.”

A Democratic aide echoed those thoughts and said the shift is indicative of a recognition that the party needs to be bolder and sharper in its proposals.

“I think there will be a lot of support for this bill,” the aide said. “It’ll make the clear contrast between the two parties on health care even more clear.”

While the Sanders proposal has gained more support among members of the Democratic conference, skeptics remain.

“The Sanders bill requires people to give up their insurance. It’s not an option that you buy in. It requires people to give up the insurance,” Sen. Claire McCaskill of Missouri said. “I’ve been down the road of requiring people to do things the government says on insurance and it is a road paved with big rocky boulders.”

Asked whether she correlates the growing support for Medicare for all to Sanders’ popularity among liberals, McCaskill — who is up for re-election in 2018 in a state Trump won easily — said she had not analyzed it from that perspective.

“I just think we’ve got to think this through and not make this some kind of political litmus test,” she told Roll Call.

While other Democratic lawmakers also said they hoped support for the Sanders bill would not be a political benchmark for the party, several openly said endorsing the concept would be crucial for any successful candidate.

“I have trouble seeing how a viable Democratic candidate does not support the idea of single-payer,” Blumenthal said. “This bill is going to drive the national message.”

Bernie-Care barrier?

Some Senate Republicans, who this summer failed in their attempt to repeal and replace the 2010 health care law, are making a last-ditch attempt to overhaul it.

Sens. Bill Cassidy of Louisiana, Lindsey Graham of South Carolina, Ron Johnson of Wisconsin and Dean Heller of Nevada are pushing legislation that would transform the health care system to essentially a large federal block grant to the states based on the size of their individual insurance pool.

Their message to the Republican conference was clear: It’s either our plan or Sanders’ proposal.

“If you want a single-payer health care system, this is your worst nightmare,” Graham said. “Bernie, this ends your dream of a single-payer health care system for America.”

Republican leadership echoed that message.

“We see what the alternative is and hopefully that’ll focus the mind,” Senate Majority Whip John Cornyn said. “Their party is clearly lurched to the left even further, and it’s made it hard for otherwise pretty pragmatic people, like Chuck Schumer, to do deals which he ordinarily would do with Republicans.”

But for Sanders, the failed attempt by the GOP to overhaul the current health care law only bolsters his case.

“To my Republican colleagues, please don’t lecture us on health care,” he said. “You, the Republican Party, have no credibility on the issue of health care.”