In a letter to Florida’s top Medicaid official in May 2015, the Obama administration said: “Coverage is the best way to secure affordable access to health care for low-income individuals. Uncompensated care pool funding should not pay for costs that would be paid for in a Medicaid expansion.”

Florida is one of 19 states that have not expanded Medicaid under the Affordable Care Act. In a report last week, the Urban Institute estimated that 730,000 to 900,000 people would gain coverage if it did. Of the 20 million people insured as a result of the Affordable Care Act, more than half have gained coverage through the expansion of Medicaid.

The Trump administration supports a House Republican bill that would repeal major provisions of the 2010 health law and eliminate funds for the expansion of Medicaid. The Congressional Budget Office estimates that the House repeal bill would reduce Medicaid spending by $839 billion in the coming decade, compared with the amount that would be spent under current law. Fourteen million fewer people would be covered by Medicaid, the office says.

Tom Price, the secretary of health and human services, has said that Medicaid has “real problems,” asserting, for instance, that one-third of doctors in the United States do not take Medicaid patients. At a recent town hall forum on CNN, Mr. Price was confronted by a cancer survivor who said he was alive because of the expansion of Medicaid. Mr. Price said the man’s experience was “not necessarily true for everybody.”

Brian Blase, a special assistant to President Trump for health care policy, has cataloged the Medicaid problems in several recent essays. In states that expanded Medicaid, he said, enrollment has substantially exceeded expectations, and spending for the new beneficiaries is “significantly above projections.”

“Expanding Medicaid was an unwise policy decision made by the drafters of the A.C.A.,” Mr. Blase wrote in Forbes in November. “The program needed reform, not expansion.”

Medicaid covers care for low-income people. The federal government and states have historically shared the costs, with the federal share averaging 57 percent. But the federal government pays a much larger share — at least 90 percent of the costs — for adults who qualify for Medicaid because of the expansion of eligibility under the Affordable Care Act.