Harold Pollack is a professor at the University of Chicago.

People protest Trump administration policies that threaten the Affordable Care Act. (DAVID MCNEW/AFP/Getty Images)

Republicans’ seven-year “repeal and replace” effort died in a fiery legislative crash two months into the Trump administration last week. Various tactical missteps helped produce this legislative failure, but the most fundamental reason the Affordable Care Act (ACA) prevailed has nothing to with the legislative tick-tock: In its own imperfect way, the ACA has insured 20 million people who would otherwise have gone uncovered. It has helped tens of millions of others who face financial or health challenges. And in doing so, it has quietly embedded itself within the fabric of American life — and has become very difficult for politicians to kill.

The GOP’s failure to take down the ACA is an object lesson in what makes a politically resilient program. As Sen. Joe Manchin (D-W. Va.) put things, voters don’t exactly know how they got coverage under ACA, but they certainly learned who was trying to take it away. The ACA brings important financial flows to individuals, states and medical providers that Congress cannot blithely disrupt without accompanying political pain. Meanwhile, aspects of the ACA solve real problems for officials in both parties. Many of these officials opposed the law when it was originally enacted. But politics is a pragmatic enterprise, and both Democrats and Republicans across the country found ways for it to serve their purposes. Thus, politicians and their constituents acquired a stake in defending the program, making it a very durable entity.

Some aspects of the ACA are more sturdy than others. The law included two main pillars that expanded health insurance coverage. The pillar most specifically derided as “Obamacare” is an ideologically moderate, fiscally disciplined market model of state insurance marketplaces popularized by conservative economists, backed by an individual mandate proposed by a Heritage Foundation scholar, and first implemented by Republican Massachusetts governor Mitt Romney. These marketplaces have faced intricate and daunting implementation problems, enjoy little bipartisan support, and have been openly and quietly undermined by Republicans. There is much speculation that the Trump administration may sabotage the marketplaces, for example by limiting important payments to participating insurers. It’s telling that few Republican politicians have spoken out on the need to bolster these arrangements.

But the second pillar — that is, the expansion of Medicaid to serve low-income individuals and families across the country — has proved surprisingly resilient. The program is popular among Republican voters in most Medicaid expansion states. More than a few Republican governors speak of the Medicaid expansion with a sense of ownership and pride, and warned Congress not to repeal these components of the ACA. Ohio Gov. John Kasich has been especially effusive, noting that “When we expand Medicaid and treat the mentally ill, they don’t live under a bridge or in a prison” and “when we take the drug addicted and we treat them, we stop the revolving door of people in and out of prisons.”

In political and human terms, Medicaid expansion is the jewel of the ACA. Within the states that embrace it, Medicaid expansion is the most important public health advance in decades. I see that every day in my work as an urban public health researcher. Most of the people I encounter in this work — people with addiction disorders, those under the supervision of the criminal justice system and homeless people — receive health care through the ACA’s Medicaid expansion. Most detainees leaving Cook County Jail are insured this way. One-third of Illinois residents living with HIV are apparently covered through the expansion, too. Federal monies reliably flow to support hospitals, safety-net providers and other key constituencies, bolster local economies, and address problems of concern to Democrats and Republican alike.

During the recent AHCA fight, Kasich and his counterparts from Michigan, Nevada, and Arkansas wrote a letter to Congress critical of the Republican House approach. Their letter was remarkable, not so much for its policy positions as for its granular understanding of the operational details. These governors show real familiarity with their Medicaid expansions, and appear all-too-cognizant of what a reversal would mean for their constituents. “It is better to get it right than go too fast,” they concluded. Fifteen Republican governors expressed concerns about the likely consequences of cutting Medicaid. Republican governors across the country have supported more-moderate approaches than AHCA that would preserve coverage in replacing ACA.

These governors’ familiarity with Medicaid expansion is visible not only in their politicking, but in their on-the-ground work, too. Our research team on the National Drug Abuse Treatment Systems Survey has been interviewing Democratic and Republican officials across the country. In our conversations, we have learned that governors are using Medicaid to address their states’ serious opioid epidemics. Governors are also using the Medicaid waiver process to tackle other challenges, too, including addressing housing needs among individuals with severe mental illness. These governors understand the partisan politics surrounding the ACA, but they also understand ways Medicaid expansion serves their own political and governing purposes. They also see that doing away with Medicaid expansion would be a disaster for the citizens they serve, and would be a political vulnerability for Republican politicians inevitably tied to that effort. Thus Medicaid expansion has earned itself bipartisan support.

Bipartisanship arises when politicians in both parties having ongoing incentives to provide support. Such incentives arise from politicians’ tactile sense that they can influence operations to serve their own goals. They also arise from politicians’ fear that they will be held accountable if things don’t go well. On this point, Kasich was admirably direct: “We don’t want to lose coverage for 700,000 people in our state.”

Thus, for the immediate future, Republican officeholders around the country will likely embrace Medicaid, even as Washington Republicans work to undermine the market-based alternative to expanded public insurance coverage. Meanwhile, Republican politicians apparently perceive few practical incentives to make private marketplace coverage really work.

Looking over the next hill, though, Republicans might want to rethink that. The more ACA marketplaces falter, the more pressure will build for their replacement, which is surely an expanded Medicare or Medicaid role. If Democrats ever succeed in enacting such a public option, Republicans will quickly feel powerful incentives to join that effort, just as they felt powerful incentives to defend Medicaid expansion. Any public option program would serve  Republican voters, who probably prefer Medicare to private coverage, and who would look to politicians of both parties to address whatever challenges arise. In that case as in this one, Republicans might find it very difficult to do away with programs once they have improved people’s lives.