Late last year, Medicaid expansion under the Affordable Care Act finally reached North Carolina, extending health security to an estimated 600,000 low-income residents. It brought the total of states that have embraced the policy to 40, leaving just 10 holdouts.

A Washington Post report added soon after, “North Carolina may be the last of the Medicaid expansion holdout states to reverse course for a while.” There was every reason to believe that was true.

But once in a while, as we’ve discussed, when it comes to the politics of health care, surprises happen. The New York Times reported:

Mississippi lawmakers reached an agreement late Monday on a proposal to expand Medicaid under the Affordable Care Act, providing largely free health coverage to an additional 200,000 low-income residents in a state with dire health outcomes and numerous rural hospitals facing financial collapse. … The agreement represents a breakthrough for Mississippi, where a coalition of hospital leaders, the broader business community, religious groups and a bipartisan bloc of elected officials have pressed lawmakers to join the 40 other states that have expanded Medicaid over the past decade.

Yes, Mississippi is a reliably “red” state. And yes, Republicans continue to control all of the levers of power, including sizable majorities in the state House and state Senate.

But on this issue, after years in which the state’s health system has struggled and hospitals have struggled to keep their doors open, there’s newfound interest in making this progressive change.

Circling back to our recent coverage, there was an unexpected breakthrough in February, when the GOP-led state House passed a Medicaid expansion bill with surprising ease — 98 to 20 — thanks in part to support from Jason White, Mississippi’s Republican state House speaker who championed the effort.

Republican Gov. Tate Reeves remained a fierce opponent of the idea — his reasoning has never made a lot of sense — but given the veto-proof margin in the state House, it didn’t much matter.

What did matter, however, was skepticism from the GOP-led state Senate, which preferred a far more conservative approach to the policy. Republican state senators in Mississippi were open to the possibility of accepting Medicaid expansion, but they wanted a less generous policy that helped fewer people.

Bicameral negotiations began, resulting in a bill that would, if approved, extend coverage to people with incomes up to 138% of the federal poverty level (roughly $20,000 a year for an individual), though Mississippians would have to work 100 hours a month to be eligible.

Success is by no means a sure thing. The compromise will still need to clear both chambers and probably overcome a gubernatorial veto. Just as importantly, as the Mississippi Free Press noted, it will be up to the Biden administration to approve the onerous and unnecessary work requirements in this proposal — and the Democratic administration has already rejected similar efforts in other states.

All of which is to say, there’s been an unexpected breakthrough in Mississippi, and that’s encouraging, but there are some difficult hurdles between here and the finish line.

As for how we arrived at this point, when the U.S. Supreme Court initially upheld the Affordable Care Act’s constitutionality, the court’s majority delivered some bad news to health care advocates: Medicaid expansion, the justices concluded, had to be optional, not mandatory under federal law.

In policy circles, many assumed this wouldn’t be too big a deal. After all, they thought, states would obviously want to do the right thing — not only for its low-income citizens, but also for its hospitals and state budgets. There are plenty of far-right ideologues and Republicans at the state level, the assumption held at the time, but they could do arithmetic. No state would choose to be so foolish as to voluntarily reject Medicaid expansion, right?

As things stand, 10 states have done exactly that — though there’s reason to believe that number might yet shrink. Watch this space.

This post updates our related earlier coverage.