THE RATE of uninsured Americans is down. The once-inexorable ballooning of health-care costs has slowed. And, the Department of Health and Human Services recently announced , U.S. hospitals are making fewer errors, adding to a previous finding that hospitals have significantly cut patient readmissions.

The Affordable Care Act isn’t responsible for all of this, but it is helping. Certainly these and other signs of progress make clear that the ACA is not destroying U.S. health care, contrary to critics’ assertions. There is no good case for the law’s repeal or modification in the ways Republican leaders have proposed. The latest news, though, does point out one of several modest changes Congress could make — if the debate on the ACA were more reasonable.

The percentage of Americans without insurance dropped by 5.3 points in the last year, the Urban Institute found this month , because of the ACA’s Medicaid expansion and health-care exchanges. The mellowing of health-care cost inflation, on the other hand, seems to have predated the ACA. Though some cost-containment measures might begin to bite in coming years, the law was more a coverage expansion policy than a cost-control policy.

One could posit that Obamacare is contributing to the improvements in hospital care, too, though even the Obama administration admits the attribution can’t be made with assurance. Fewer patients are falling, getting pressure ulcers from lying in bed or acquiring catheter-related infections. HHS estimates that these trends saved some 50,000 lives between 2011 and 2013. Hospitals are also getting better at checking up on patients after they are discharged. The 30-day readmission rate has dropped 1.5 percentage points since 2011.

One plausible explanation for these trends is that the ACA contributes by having changed the way hospitals are paid for treating patients with hospital-acquired conditions. The law also punishes hospitals with high readmission rates. Less coercive is an Obama administration program to collect and disseminate strategies to cut hospital errors. The Urban Institute’s Bob Berenson argues that, unlike other programs, the measures used here are fairly straightforward and, though the financial penalties involved aren’t harsh, just shining a bright and sustained light on them should be helping.

Still, experts have pointed out that the government can’t be sure what’s really making the difference at hospitals. There’s also concern that hospitals in low-income areas will be punished because they tend to have higher readmission rates no matter how conscientious they are. Mr. Berenson argues that the way hospitals are evaluated under the program should change. Instead of punishing hospitals in the bottom half of the readmissions list, lawmakers could punish those that don’t show improvement or adjust payments for treatments on readmitted patients.

This is the sort of change that, in a more rational political environment, Congress would be evaluating, instead of continuing to fight the same, tired ideological war over Obamacare.