WASHINGTON — States that have aggressively put the Affordable Care Act into practice have cut the number of uninsured residents sharply — in some cases in half or better — while those that balked have improved little if at all, according to new data released Tuesday.

The state-by-state numbers, from Gallup’s Healthways Well-Being Index, reinforce one of the major impacts of ObamaCare so far: Political debate has widened the health care gap between red and blue states.

All 10 states with the largest percentages of uninsured adults now have Republican governors and legislatures. The lowest percentages all are governed by Democrats, with the exception of Pennsylvania.

The 10 states with the biggest improvement in insurance coverage all took two major steps to implement the health care law — they expanded Medicaid coverage, as the law allows, and they either set up their own online marketplace to let residents buy insurance or they entered into a partnership with the federal government to create one.

By contrast, the states that still have the highest percentages of uninsured residents all declined to expand Medicaid and refused to participate in creating the online exchanges, leaving that task to Washington.

Nationwide, 18 percent of Americans lacked insurance last year just before the health care law took effect, while 13.4 percent were uninsured in the second quarter of this year, according to Gallup’s surveys.

Arkansas and Kentucky, both states that began with large numbers of uninsured residents, showed the biggest improvements. In Arkansas, the percentage of residents without insurance dropped from 22.5 percent last year — significantly above the national average — to 12.4 percent at the middle of this year. Kentucky improved from 20.4 percent uninsured to 11.9 percent.

At the other end of the scale, Texas had the highest percentage of uninsured residents last year — nearly 3 in 10 — and still does. The share of uninsured Texans dropped by only 3 points, to 24 percent.