About a week ago, Sen. Kamala Harris (D-Calif.) raised a few eyebrows when she announced she’d sign on as a co-sponsor to Sen. Bernie Sanders’ (I-Vt.) “Medicare for All’’ bill. As the California Democrat said at a town-hall meeting in Oakland, she sees a single-payer system as “the right thing to do.”

The Boston Globe reports that Sen. Elizabeth Warren (D-Mass.) apparently agrees.

Senator Elizabeth Warren said Thursday she will support Bernie Sanders’ single-payer health care plan, thrilling liberals who see the legislation as the next major battle for the soul of the Democratic Party. The Massachusetts Democrat described the bill as expanding Medicare, the government insurance that covers people age 65 and older, to all Americans. She said it would guarantee care for everyone at the lowest prices, and she downplayed an emerging split between liberals and Democratic centrists over such a massive expansion of a government-run program.

The Globe article added that Massachusetts’ other senator, Democrat Ed Markey, also intends to sign on.

It’s worth noting that Sanders’ proposal has not yet been introduced, which means we don’t yet have any legislative details or a full list of the bill’s co-sponsors. That said, we know it’s a single-payer plan and we know that this approach has growing acceptance in the Democratic mainstream, which is itself pretty remarkable.

Sen. Chris Murphy (D-Conn.), meanwhile, is moving forward with a related proposal, which as Politico noted yesterday, would allow “every individual and business buy into Medicare as part of Obamacare’s exchanges.” It’s not single-payer, but because Medicare is a socialized system, it’d be a significant step in a progressive direction – and offer an interesting alternative to lawmakers who aren’t yet on board with Sanders’ model.

I wonder if Republicans fully appreciate their role in creating these political conditions.

It’s often overlooked, but the Affordable Care Act was, by many metrics, the center-right approach to health care reform when Barack Obama and congressional Democrats crafted the system eight years ago. Far-right hysterics notwithstanding, “Obamacare” is compromised almost entirely by provisions that were designed to garner bipartisan support.

It is, after all, extremely similar to the model Mitt Romney created when he was a governor.

And yet, Republicans nevertheless decided it was a dangerously radical, left-wing government takeover, threatening the fate of the nation and the free-enterprise system. GOP officials decided that ACA destruction would be one of their party’s principal goals, and while that hasn’t worked out especially well, Republicans nevertheless made one thing perfectly clear: Democrats may be comfortable with a moderate reform model, but today’s GOP is not.

More than a few progressives interpreted this in an interesting way: if Republicans won’t accept a health care system designed to be bipartisan, Democrats don’t have much of an incentive to try to meet the GOP in the middle. In other words, many Dems effectively concluded, “If Republicans aren’t prepared to work with us on a consensus model, we might as well pursue the policy we actually want.”

Just like that, Bernie Sanders found he has more allies than he expected to have.