The passage of the Affordable Care Act was supposed to reduce the number of working-age adults without health insurance. But in Maine, according to recent research, the ranks of the uninsured haven’t diminished over the past few years. That doesn’t mean it’s the Affordable Care Act that’s not working.

To make a huge, positive difference in the lives of the thousands of Mainers who still lack coverage, legislators should pass the latest proposal before them to take full advantage of the federal program and expand Medicaid eligibility.

The report on uninsured rates in Maine was released Monday by the Maine Health Access Foundation. The number of Mainers enrolling in insurance plans under the ACA started strong in 2014 and continues to grow, reaching nearly 75,000 last year.

But the percentage of uninsured Mainers has held steady since 2013 at about 15 percent, the nonprofit advocacy group concluded, based on an annual state survey of Mainers’ health habits. During the same period, the number of people receiving MaineCare (as Maine’s Medicaid program is known) shrank as tighter standards were put in place.

Those most likely to be uninsured? Men, young adults, people without a high school diploma and residents of rural areas, the report found.

The downsides to lacking insurance? Compared to people with coverage, the uninsured are more likely to put off preventive care or skip it altogether. So when they do get treated, caring for them is more expensive and more complicated.

The ACA’s solution? Providing states with funds to expand Medicaid eligibility. The U.S. government would pick up 100 percent of the tab through 2016, gradually reducing that to 90 percent by 2020.

Gov. Paul LePage and most Republicans in Augusta have stood firm against Medicaid expansion. But they’re not taking into account its benefits.

In states that have gone along with expansion, the share of uninsured patients in hospitals has fallen from 12 percent to 6 percent — meaning that hospitals have more to spend on research and improving the quality of care. And facilities in expansion states have had “substantially greater declines” in the tab for uncompensated care than their counterparts elsewhere, researchers for the Robert Wood Johnson Foundation found.

Meanwhile, Tom Saviello and Roger Katz, the moderate Maine Republican state senators who are collaborating on another attempt at expanding MaineCare eligibility here, note that it would help finance the growth of substance abuse treatment facilities — which are desperately needed to address Maine’s raging heroin epidemic.

MaineCare expansion makes sense for both economic and humanitarian reasons, and legislators should channel their energy into reaching a compromise that will let them move ahead with the program. The well-being of people across the state is at stake.