The Monday night collapse of Mitch McConnell’s Better Care Reconciliation Act has many causes, but the least discussed, and most important, is this: Obamacare is working, and that’s why the Republican replacement effort is failing.

We have gotten used to discussing the Affordable Care Act mainly in terms of its problems, and those problems are real. There are pockets of the country in which it is working poorly. Deductibles are too high, and premiums are volatile. The Trump administration has worked hard to sabotage the insurance exchanges and drive insurers out of the marketplaces.

But focusing on the problems obscures the overwhelming reality: The Affordable Care is popular, it is working, and on every dimension that voters care about, it outperforms the Republican alternatives. And that makes it damn hard to replace.

Poll after poll shows more people now favor the Affordable Care Act than oppose it. It has higher approval ratings than Donald Trump, Mitch McConnell, Paul Ryan, or the Republican Party. It far outperforms the Republican replacement plans: A new Washington Post/ABC News poll found voters prefer Obamacare to the Republican health bill by a 2-to-1 margin — 50 to 24 percent. You rarely see numbers like that in American politics.

These numbers are strange if you listen to Republicans describe the Affordable Care Act. In their telling, it is always “imploding,” “failing,” “dying,” “disastrous.” How can a law in such crisis command such healthy public support? The answer is that the law is, for the most part, not in crisis. There are areas of the country where the exchanges have struggled to attract insurers, and there are markets in which premiums have increased rapidly. These problems are real and, if the party in power were interested in improving the law, solvable.

But even without improvements, the reality is that for most people, in most places, the Affordable Care Act is working. The bulk of its coverage expansion has been through Medicaid, which is immune to the problems of the insurance marketplaces. Surveys find that Medicaid enrollees really like their coverage; they’re just as satisfied as people who get health insurance at work. Indeed, the Medicaid expansion has proven so popular, and so effective, that Senate Republicans from Medicaid-expanding states like Ohio and Nevada have been fighting to preserve it.

Nor are the exchanges in anything close to a state of collapse. More than 10 million people are buying insurance off Obamacare’s exchanges, and surveys show most of them are happy with their plans. While there are some counties at risk of beginning 2018 without participating insurers, the total number is quite small — 38 out of 3,143 counties, according to the Kaiser Family Foundation.

Nor has the Affordable Care Act seen exploding costs either in the program or in the health care system more broadly; the ACA has cost less than the Congressional Budget Office expected, and spending growth in the health system overall has been at historic lows (an achievement for which Obamacare deserves some, though not all, of the credit). Cost control in the health system has been so unexpectedly effective that the government is now projected to spend less on health care with Obamacare than we were projected to spend without Obamacare.

This is the reality that Republicans are flinging their repeal effort against — and it is a reality that their plans mostly worsen. According to the Congressional Budget Office, over the next 10 years, 23 million fewer people would have insurance if the House health bill passed, 22 million fewer people would have insurance if the Senate health bill passed, and 32 million fewer people would have insurance if the 2015 repeal bill — which McConnell now wants to bring to a vote — passed.

Obamacare’s biggest problem is the high cost sharing that frustrates those who buy coverage on the marketplaces. But all of the Republican bills would lead to higher deductibles, higher copays, sparer insurance, and, on an apples-to-apples basis, higher premiums. The reasons for this are simple: The GOP bills cancel the individual mandate, which pushes young and healthy people to buy health insurance, and then take hundreds of billions of dollars Obamacare is currently spending to make insurance more affordable and spend it instead on tax cuts and deficit reduction.

If the Affordable Care Act were truly as bad as Republicans say it is, it would be easier to replace. Hell, if it were as bad as they say it is, straight repeal would be an improvement — but even conservative Republicans don’t dare discuss repeal without some kind of vague, wonderful replacement.

The most concise description of GOP health policy thinking was President Donald Trump’s promise to repeal Obamacare and replace it with “something terrific.” But every time Republicans offer up an actual replacement, it dramatically, embarrassingly underperforms the Affordable Care Act. Republicans have spent years complaining that the Affordable Care Act covers too few people with insurance that costs too much and covers too little. But they have not managed to come up with a replacement that covers even as many people with insurance that costs less.

Could the American health care system be better than it is today? Of course. But it could also be much worse. And so far, much worse is what Republicans have offered. The reality is that Obamacare took many of their best ideas on health care, the GOP remains divided on what its health care policies are even meant to achieve, and the result has been a disastrous process that has created appallingly cruel and unworkable legislation.

But make no mistake: The Republican failure to craft an effective replacement for Obamacare isn’t an accident. It’s a function of the fact that Obamacare is largely working, and Republicans who spent years persuading themselves and their base it’s a catastrophic failure are now slamming into that reality.