Former Sen. Max Baucus (D-Mont.), a fiscal moderate who, as chairman of the Senate Finance Committee, presided over the passage of the Affordable Care Act, expressed his support on Thursday for the creation of a single-payer health care system.

“My personal view is we’ve got to start looking at single-payer,” Baucus said in remarks at Montana State University, according to the Bozeman Daily Chronicle. “I think we should have hearings... We’re getting there. It’s going to happen.”

Single-payer health care, in which the federal government insures all citizens through one large program, is a model for universal coverage in many developed countries, including Canada, France and Australia. But it has long been viewed as a pipe dream in the United States, where a plurality of people receive coverage from their employers.

Baucus’ endorsement of the idea speaks to just how dramatically the health policy debate has shifted within the Democratic Party in recent years ― particularly since the 2016 presidential run of Sen. Bernie Sanders (I-Vt.), who made what he called “Medicare for all” a central issue of his campaign.

Baucus was the subject of progressive frustration for his stewardship of the ACA, also known as Obamacare. Critics argued that he held the bill in committee far too long in hopes of winning the support of moderate Republicans who did not end up voting for the final bill. The lengthy negotiation period he initiated gave Republicans much-needed time to mobilize opposition to reform, according to Baucus’ detractors.

Obamacare itself relies on a hybrid model, once favored by conservative policy experts, that combines the creation of a new private, individual insurance marketplace and an expansion of Medicaid.

Given Baucus’ history as a fiscal moderate active in the ACA’s passage, his positive remarks about single-payer could provide a boost to progressive activists agitating for its implementation.

As Senate Finance Committee chairman, Baucus ruled out consideration of single-payer from the beginning, and declined to invite the testimony of single-payer advocates at hearings. The latter decision prompted disruptive protests from activists, and Baucus later said that he regretted not engaging more with the policy’s proponents.

In September 2009, Baucus also voted against two amendments that would have created a public health insurance option on the Obamacare individual insurance exchanges.

Baucus kept single-payer off the table during the development of Obamacare because he believed the country was not ready for it at the time, he told NBC News on Friday.

“I just think the time has come,” Baucus said. “Back in ’09, we were not ready to address it. It would never have passed. Here we are nine years later, I think it’s time to hopefully have a very serious good faith look at it.”

Sen. Jon Tester (D-Mont.), a moderate who represented Montana alongside Baucus from 2007 to 2014, also expressed openness to single-payer this week.

“Maybe it’s something we should, quite frankly, take a solid look at,” Tester said Wednesday.

Tester does not support single-payer legislation, however. When Sen. Steve Daines (R-Mont.), aiming to put Democrats in an awkward political position, introduced a trick amendment creating a single-payer system to the Obamacare repeal bill, most Democratic senators voted “present” on the motion, but Tester was one of four Democratic senators to vote “no” on it.

Former Sen. Kent Conrad (D-N.D.) ― a moderate who vehemently opposed creating a public health insurance option during the passage of Obamacare ― told HuffPost that unlike Baucus, he believes it is “unlikely we will get a single-payer system in the foreseeable future.”

Single-payer is improbable, Conrad argued, because funding a federal health insurance program would cost taxpayers so much and because medical providers are so opposed to radically transforming the system.

Instead, he said, the “best system combines universal coverage with private not-for-profit insurance with the government assisting those who cannot afford insurance.”

He also favors empowering Medicare to negotiate bulk discounts on prescription drugs, just as the Veterans Affairs health care system does.

Kim Kyung Hoon / Reuters Former Sen. Max Baucus (D-Mont.) now says he supports the creation of a fully public federal insurance program.

In addition to Sanders’ presidential run, the collapse of Republican efforts to repeal Obamacare has increased grassroots energy behind single-payer as activists seek to go on the offensive. Progressive pressure groups like Credo have launched efforts to make support for the policy a litmus test for 2020′s Democratic presidential candidates.

Single-payer now has more support in Congress than at any other time in recent history. Single-payer legislation introduced by Rep. John Conyers (D-Mich.) has more co-sponsors than ever, with the support of a majority of the House Democratic Caucus.

Sanders plans to unveil a much-anticipated version of single-payer legislation next Wednesday. Sens. Kamala Harris (D-Calif.), a rumored 2020 presidential contender, and Elizabeth Warren (D-Mass.) have already announced plans to co-sponsor the bill.

Polling suggests that the idea of single-payer is popular with the public, especially among Democrats. In a May 2016 Gallup poll, 58 percent of Americans and 73 percent of Democrats said they supported replacing “the ACA with a federally funded healthcare program providing insurance for all Americans.”

Even elected Democrats who remain wary of single-payer have begun trying to capitalize on the ambitious proposal’s popularity. The Congressional Hispanic Caucus’ political action committee, Bold PAC, has repeatedly alluded to the “Medicare for all” fight in fundraising e-mails ― even though half of the 30 CHC members have yet to actually endorse single-payer, and the PAC does not make support for the policy a condition for its financial support.

Of course, it is much easier to talk about single-payer than to actually implement it. Replacing the current system with one large federal program would require a massive tax increase in exchange for what advocates believe would result in net cost reductions thanks to the government’s considerable bargaining power.

It would also force the nearly half of Americans who get insurance from their jobs to enroll in a new government program. Given the outcry that Obamacare elicited for canceling the plans of a fraction of that number of people, enacting single-payer would likely prove an extraordinary political challenge.

In the meantime, though, the excitement around single-payer has already widened the spectrum of acceptable debate about health care. Expansions of coverage that once seemed radical now seem downright moderate by comparison. In August, Sen. Brian Schatz (D-Hawaii) announced plans to introduce legislation allowing Americans of all ages and incomes to buy into Medicaid. And earlier this week, Sen. Chris Murphy (D-Conn.) revealed his intention to introduce a bill creating a comparable universal buy-in option for Medicare, which he said “may be the fastest way to a single-payer system.”

This article has been updated with comments from Tester and Conrad, as well as additional comments from Baucus.