More than two and a half years have gone by since the Affordable Care Act, a.k.a. Obamacare, went fully into effect. Most of the news about health reform since then has been good, defying the dire predictions of right-wing doomsayers. But this week has brought some genuine bad news: The giant insurer Aetna announced that it would be pulling out of many of the “exchanges,” the special insurance markets the law established.

This doesn’t mean that the reform is about to collapse. But some real problems are cropping up. They’re problems that would be relatively easy to fix in a normal political system, one in which parties can compromise to make government work. But they won’t get resolved if we elect a clueless president (although he’d turn to terrific people, the best people, for advice, believe me. Not.). And they’ll be difficult to resolve even with a knowledgeable, competent president if she faces scorched-earth opposition from a hostile Congress.

The story so far: Since Obamacare took full effect in January 2014, two things have happened. First, the percentage of Americans who are uninsured has dropped sharply. Second, the growth of health costs has slowed sharply, so that the law is costing both consumers and taxpayers less than expected.

Meanwhile, the bad things that were supposed to happen didn’t. Health reform didn’t cause the budget deficit to soar; it didn’t kill private-sector jobs, which have actually grown more rapidly since Obamacare went into effect than at any time since the 1990s. Evidence also is growing that the law has meant a significant improvement in both health and financial security for millions, probably tens of millions, of Americans.