The Affordable Care Act was an imperfect and incomplete reform. The political compromises needed to get it through Congress created a complex system in which too many people fall through the holes. It was also underfunded, which is why deductibles are often uncomfortably high. And the law has faced sabotage both from G.O.P.-controlled state governments and, since 2017, the Trump administration.

Despite all that, however, the act has vastly improved many Americans’ lives — and in many cases, saved lives that would otherwise have been lost due to inadequate care. The progress has been most dramatic in states that have tried to make the law work. Before the A.C.A. went into effect, 24 percent of California adults too young for Medicare were uninsured. Today that number is down to 10 percent. In West Virginia, uninsurance fell from 21 percent to 9. In Kentucky, it fell from 21 to 7.

Over all, around 20 million Americans who wouldn’t have had health insurance without the A.C.A. now do.

At the same time, none of the dire predictions conservatives made about the law have come true. It didn’t bust the budget — in fact, deficits came down steadily even as the A.C.A. went into effect. It didn’t discourage workers from taking jobs: Employment of Americans in their prime working years is back to what it was before the financial crisis. And despite Donald Trump’s best efforts to undermine it, the system isn’t in a “death spiral”: Insurers are making money and premiums have stabilized.