The HealthCare.gov federal insurance exchange website in 2013. (KAREN BLEIER/Agence France-Presse via Getty Images)

IN ANY other February, the Obamacare enrollment numbers released last month would have been big news. The Department of Health and Human Services announced that 12.7 million people had chosen health-care plans in the exchanges the law set up — far more than the 10 million HHS predicted would have exchange-based insurance in 2016. The number will likely go down, as some people fail to pay their premiums; the best case, according to the Kaiser Family Foundation’s Larry Levitt, is that about a million more people will be covered in 2016 relative to last year.

These figures leave the Affordable Care Act in an awkward place. It has achieved its primary goal — reducing the rate of uninsured Americans — by cutting the number of people without insurance by 16 million since 2013. But the number of people participating in the markets it set up is not as large as some had predicted — or hoped. The Congressional Budget Office projected that some 21 million people would have insurance through the exchanges in 2016. The law is by no means failing, but higher exchange enrollment would help ensure that the insurance markets were stable and sustainable.

The optimistic view is that enrollment is climbing and will continue to do so, only at a slower-than-anticipated rate. In the early months of the ACA’s rollout, President Obama allowed some people to keep their old plans. That accommodation will end by next year, boosting enrollment in the law’s marketplaces. Also, the law’s penalty for failing to have insurance coverage is set to ramp up dramatically.

A Kaiser Family Foundation analysis of premium hikes in major cities found that insurance-buyers on the ACA’s marketplaces face an average premium increase of 3.6 percent this year — not double digits — and that number does not factor in federal subsidies. Though some parts of the country are seeing more price volatility, that is in part because insurers are still learning what their customers’ health needs are and how to compete against each other in the exchanges.

The pessimistic view is that, without further enrollment gains, some places may end up without healthy, competitive insurance markets. This may be particularly true of less populated parts of the country that insurance companies never served well. Insurance companies complain about high costs in some places, and this Congress will not provide them with any more assistance. If insurers abandon tough markets, some insurance customers may be underserved under a law that was supposed to nudge the country very close to universal coverage.

The solution is to focus on keeping enrollment growing, as bringing more people into the system helps spread costs and attracts insurers into competing for business. Many people still do not know they are eligible for federal help in buying insurance coverage. There are no doubt others who do not know that the penalty for going without insurance is increasing. Simple outreach, along with fixing some minor technical issues that continue to frustrate insurance-buyers, could help. A different Congress would debate nudging up premium subsidies, increasing the penalty or both. Wholly unhelpful, though, are the constant calls to defund or repeal a law that has made great progress — and could do much more good if more politicians gave it a chance.