One of the fiercest fights happening within the Republican Party right now is what to do about Obamacare’s Medicaid expansion.

The Affordable Care Act broadened Medicaid eligibility to cover millions more low-income Americans, and offered states federal money to recoup the costs.

But only 16 states with Republican governors expanded Medicaid, including Ohio’s John Kasich, who recently met with Trump and has advocated continuing expansion. Seventeen governors rejected the option, though, often with the justification that Medicaid doesn’t actually improve people’s health.

So does it? With 10 million people in the program right now, and the future of the ACA at stake, the question seems worth parsing.

We actually have some pretty good data out of Oregon about Medicaid’s effects on health. There, researchers from Harvard tracked what happened to the winners and losers of a state lottery that offered Medicaid to 10,000 randomly selected Oregonians in 2008. This is the closest we have to a randomized trial on health insurance — the gold-standard study methodology — so it’s been a treasure trove of information for researchers. The study also gives us a pretty good picture of how exactly Medicaid impacts people’s health — and where it falls short……more