Missouri was once considered a battleground state in national elections, but not anymore. The last Democratic presidential candidate to win there was Bill Clinton in his romp to reelection in 1996; Donald Trump won the state in 2016 by 19 points.

But on Tuesday, when asked to weigh in on the most hard-fought policy war of the last decade, Missouri’s voters turned their backs on the Republican Party and embraced the Democratic position. Over the objections of the Republican governor, Republicans in the state legislature and Republicans everywhere, they voted to amend the state’s constitution to finally accept the expansion of Medicaid provided under the Affordable Care Act, a.k.a. Obamacare.

This is not just a story about one conservative state. It contains an important lesson for Democrats, one they should not forget if they win control of the federal government in November.

Although it got less attention than other provisions when the ACA passed in 2010, the expansion of Medicaid may have been the most significant thing the law did, providing health coverage to millions of Americans. Under the status quo, each state set eligibility for the joint federal-state program, which in practice meant that liberal states provided insurance to most poor people and Republican states restricted the program to as few people as possible.

For instance, Texas sets eligibility for adults at 15 percent of the federal poverty level, so if you’re in a family of four and you earn more than a princely $3,930 a year, you’re too rich to get Medicaid. Which is a big reason that even before the pandemic, about 5 million Texans lacked health coverage.

So under the ACA, Medicaid would be expanded to the same level everywhere, with anyone making less than 133 percent of the poverty level ($34,846 for a family of four) eligible for coverage. But in 2012 — in a decision born more of horse-trading among justices than constitutional analysis — the Supreme Court ruled that states could opt out of the expansion if they wished.

And in Republican-run states, they did indeed wish. It didn’t matter that the federal government would pick up 90 percent of the cost, or that study after study showed that accepting the expansion boosted state budgets and economic growth. Deep-red states simply refused, not only because letting poor people have health coverage ran against conservative ideology, but because the law had “Obama” right there in the nickname. They’d be damned if they’d allow their constituents to benefit from it.

Yet many of the law’s supporters remained optimistic. Over time, they believed, even die-hard Republicans wouldn’t be able to resist all that federal money and the opportunity to make their states less miserable.

But things turned out to be more complicated than that. Republican officeholders’ loathing of President Barack Obama was nearly infinite, as was their eagerness to force people to suffer for the sin of being poor.

But then something unexpected happened. The voters — even Republican voters — got fed up.

It turned out that Medicaid is a hugely popular program. Not only do majorities of Americans think it works well, but according to recent polling from the Kaiser Family Foundation, two-thirds of Americans have either used it themselves or have friends or family who have. And in those red states that have yet to accept the expansion, 61 percent of people say their state should do so.

Missouri is only the latest state where voters overruled their conservative elected officials. A month ago, voters in Oklahoma passed a similar measure. In 2018, measures passed in Idaho, Nebraska and Utah. There are now 12 remaining states that have yet to accept the expansion.

Over the long term, there’s a simple solution to this problem: create a universal system that covers everyone, so we can stop arguing about whether certain people and not others deserve health coverage. But on the way to that day, Democrats should be guided by the fact that the public is on their side.

After the long trauma of the battles over the ACA, it can be easy to forget. And yes, Republicans are very effective at demagoguing anything having to do with health care (remember “death panels”?). But there are some very simple facts that ought to steel Democrats’ spines.

Most Americans like government health-care programs — Medicare, Medicaid, CHIP, Veterans Affairs — which is why Republicans pretend to support them, too. When given a choice, people want those programs to be larger and more comprehensive, not smaller and stingier.

And it’s not just health care. On issue after issue, the public is on Democrats’ side, whether it’s climate change, the minimum wage, tax increases on the wealthy, marijuana legalization, immigration or guns. If they displayed half the confidence that Republicans do in their unpopular positions, they’d never lose a national election.

The Trump administration’s disastrous mishandling of the coronavirus pandemic has created an opportunity, showing how important government is and how vital it is that it work properly. And if Democrats take over in 2021, they should remember, when Republicans start bleating about the dangers of “socialism,” that even the GOP’s own constituents aren’t buying what they’re selling.

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