On the eve of Senate Democrats rolling out their most prominent single-payer health care plan to date, even the conference’s most conservative member says the idea is at least worth a look.

Sen. Joe Manchin (D-WV) told Bloomberg that he was open to exploring a single-payer health insurance program.

"It should be explored," he said. "I want to know what happens in all the countries that have it — how well it works or the challenges they have."

He clarified his position in a later statement.

“Once we address the short-term stability of the market, we should look at all ideas to fix the long-term problems facing our healthcare system,” Manchin said. “I am skeptical that single-payer is the right solution, but I believe that the Senate should carefully consider all of the options through regular order so that we can fully understand the impacts of these ideas on both our people and our economy.”

Manchin is maybe the least likely Democrat to even flirt with single-payer. He’s conservative himself, represents West Virginia, where two-thirds of voters backed Donald Trump in 2016, and is facing a tough reelection race next year as the top target for Republicans.

Nevertheless, he’s not ruling it out. It’s a reminder of how much the Democratic Party is drifting toward a universe where single-payer health care is the default position.

The Democratic Party wants to move further left than Obamacare

Even those who aren’t yet on board with Sen. Bernie Sanders’s forthcoming Medicare-for-all legislation are proposing ideas that would expand the government’s role in health care. Sen. Brian Schatz (D-HI) has a bill to allow people to buy into Medicaid. Sen. Chris Murphy (D-CT) is proposing to let people and business buy into Medicare. At the very least, senators like Debbie Stabenow (D-MI) want to allow older Americans not yet eligible for Medicare to join the program.

Sanders’s bill, meanwhile, is winning wide support from senators — like Connecticut’s Richard Blumenthal and Wisconsin’s Tammy Baldwin — who wouldn’t necessarily be the first people you’d expect to back it.

Perhaps most importantly, as Vox’s Dylan Matthews wrote, any Democratic senator with ambitions about running for president in 2020 is backing Sanders: Elizabeth Warren (MA), Kamala Harris (CA), Cory Booker (NJ), and Kirsten Gillibrand (NY) among them.

Here’s how Matthews put it:

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.

With Manchin at least taking single-payer health care under advisement, any remaining Democratic resistance to the idea seems to be crumbling.