Personalities surely mattered. Louisiana’s re-elected John Bel Edwards was widely liked, Kentucky’s defeated Matt Bevin widely disliked. Demography probably also mattered. Urban and especially suburban voters have turned hard against Trump, but rural voters haven’t, at least so far — and Mississippi is one of the few states left with a majority-rural population.

But there’s another difference among the three states. Kentucky and Louisiana took advantage of the Affordable Care Act to expand Medicaid, leading to steep drops in the number of uninsured residents; Mississippi hasn’t. This meant that voting Democratic in Kentucky and Louisiana meant voting to preserve past policy success, while the same vote in Mississippi was at best about hope for future reform — a much less powerful motivator.

Back in 2010, as Obamacare was about to squeak through Congress, Nancy Pelosi famously declared, “We have to pass the bill so that you can find out what is in it.” This line was willfully misrepresented by Republicans (and some reporters who should have known better) as an admission that there was something underhanded about the way the legislation was enacted. What she meant, however, was that voters wouldn’t fully appreciate the A.C.A. until they experienced its benefits in real life.

It took years to get there, but in the end Pelosi was proved right, as health care became a winning issue for Democrats. In the 2018 midterms and in subsequent state elections, voters punished politicians whom they suspected of wanting to undermine key achievements like protection for pre-existing conditions and, yes, Medicaid expansion.

And this political reality has arguably set the stage for further action. At this point, as far as I can tell, all of the contenders for the Democratic presidential nomination are calling for a significant expansion of the government’s role in health care, although they differ about how far and how fast to go.