Among adults age 18 to 64, the uninsured rate for Hispanics is now about 17.9 percentage points higher than for whites, down from a difference of 26 percentage points in 2013, according to the National Center for Health Statistics. And the uninsured rate for blacks is 4.6 percentage points higher than for whites, compared with a gap of 10.4 points in 2013.

Before the Affordable Care Act, large numbers of Hispanics were uninsured, in part because many had low-wage jobs that did not offer insurance. Even with the health care law, many Hispanics are ineligible for Medicaid and insurance subsidies because of their immigration status.

Still, the overall rate of Hispanics without health insurance is down to 16 percent, from 24.4 percent in 2013. The rate of uninsured African-Americans has dropped only slightly less dramatically, to 10.5 percent from 15.9 percent in 2013, according to the Census Bureau.

Dr. Satcher said the gains in coverage are also threatened by cuts in federal subsidies paid to insurance companies on behalf of low-income people and by provisions of the Republican tax bill that would, in effect, eliminate the requirement for people to have coverage.

Demand for health insurance through the Affordable Care Act marketplaces has remained strong during this enrollment period — sign-ups were running ahead of the same period last year, even in states like New Jersey, where Republican governors have been lukewarm about promoting the health law. But because the enrollment period in the HealthCare.gov marketplace was half as long, the overall number of people who sign up is expected to be lower than in the last couple of years. (A preliminary tally is likely to become available next week.)

The effects of the federal cuts on minority residents are evident in the work of the Center for Family Services, which serves seven counties over 3,000 square miles in southern New Jersey.

The nonprofit had its federal funding cut by 64 percent, reducing the number of navigators from 21 who spoke six languages between them to 6 who speak English and Spanish. As a result, it stopped doing enrollment at several locations in Camden, a poor and majority black and Hispanic city.