The number of Americans enrolled in the Affordable Care Act’s health insurance marketplaces has roughly doubled since President Biden took office, but White House officials warned Wednesday that the surge in Americans taking advantage of increased government health care subsidies could face risks as President-elect Donald J. Trump returns to office.
Nearly 24 million Americans, a record, have already signed up for plans under the program, popularly known as Obamacare, during the current enrollment period, according to the White House.
Those gains have been driven in part by major federal subsidies that helped shave the cost of premiums across income groups. Those subsidies, approved by Mr. Biden and Democratic lawmakers, are set to expire this year.
In a statement, Mr. Biden called on Congress to “double down on the progress we have made” by extending them.
As Republicans assume control of the Senate and the House, it is unclear whether those subsidies, which come in the form of tax credits, will be renewed without significant compromise.
Some key congressional Republicans have cast doubt on an extension. Mr. Trump has not outlined a health care strategy for his second term, and has spoken vaguely about the Affordable Care Act when asked if he would again seek to overturn the law, as he did in when he first became president in 2017.
Mr. Trump’s campaign said it did not support the increased subsidies, which make insurance effectively free for many lower-income people and decrease premiums for higher-earning households.
Mr. Biden’s chief domestic policy adviser, Neera Tanden, told reporters on a conference call on Tuesday that “our efforts to lower health care costs and expand coverage are in jeopardy.”
Under the Affordable Care Act, Americans had been eligible for financial assistance on a sliding scale based on income. But Mr. Biden and Democrats approved more federal assistance and expanded who was eligible for it, allowing people who make more than 400 percent of the federal poverty level, or roughly $120,000 for a family of four, to qualify.
The Congressional Budget Office last month estimated that premiums would spike without a permanent extension of the enhanced subsidies, and the number of uninsured Americans would go up by more than two million in 2026, 3.7 million in 2027 and then 3.8 million each year on average through 2034.
Wednesday’s announcement was part of a broader effort by federal officials to highlight the Biden administration’s health policy on its way out, including a new Medicare drug price negotiation program, an expansion of drug addiction treatment and gains in Medicaid coverage for new mothers.
The Affordable Care Act has transformed the American health system, covering roughly 50 million Americans at some point over the last decade, slashing the uninsured rate among minority groups and expanding access to Medicaid, the joint federal-state insurance program for the poor.
Conservative lawmakers and health policy experts have said that the subsidies, which the Congressional Budget Office has said would cost more than $300 billion over the next decade, are an exorbitant way to boost the health insurance marketplaces, which they have criticized for offering mediocre health coverage.
A spokesman for Representative Brett Guthrie, a Kentucky Republican who leads the key House Committee on Energy and Commerce, pointed to skeptical comments Mr. Guthrie made last month suggesting that the subsidies increased health spending. Representative Jason Smith, a Missouri Republican who led the House Ways and Means Committee last year, and Representative Jodey Arrington, a Texas Republican who led the House Budget Committee, have described a proposed renewal as “unconscionable.”
Some conservative critics of the policy have alleged that Americans are benefiting from subsidized coverage above the amount they are entitled to. Asked about whether those claims were true, federal officials on Tuesday defended their process to verify that those who apply for and receive subsidized coverage have submitted accurate information about their income.
The subsidies have also been a boon for health insurers, which could lose billions if they expire. They have rallied with patient advocacy groups to push lawmakers for an extension.
Cynthia Cox, an Obamacare expert at KFF, a nonprofit health care research group, said that the politics of the subsidies were complicated for Republicans because of how much of the growth in the marketplaces was concentrated in southern, Republican-led states, where people in rural areas with few health coverage options would see enormous increases in premiums if they lapsed.
“The kind of demographics and the geographical distribution of who’s signing up and who’s benefiting from the enhanced subsidies make it so that it’s possible that some Republicans might see a benefit to their constituents if they renew the subsidies,” she said.
Some Republican leaders, including Senator Bill Cassidy of Louisiana, who is set to lead the chamber’s health committee, have suggested that they could compromise with Democrats to do so.
Senator Lisa Murkowski of Alaska, a more moderate Republican, recently told the Northern Journal, an Alaska newsletter, that Congress needed to extend the subsidies.
“I worry a little bit that it’s going to be one of these, ‘We’re just going to throw everything out. We didn’t like those, and so we’re going to let these expire,’” she said, referring to the legislation that approved the increased subsidies. “I look at this, and I would make the argument that you’ve got a lot of folks that have seen some real relief.”
Democrats in December unsuccessfully worked to insert a one-year extension of the subsidies in a year-end spending package, but they have vowed to press on in budget negotiations early this year.
“This is a major, major, major, major priority,” said Representative Lauren Underwood, an Illinois Democrat who has introduced legislation that would permanently extending the tax credits. Without the same kind of subsidized coverage, Americans who had signed up for cheaper plans in recent years “are going to be shocked, and they’re going to be mad,” Ms. Underwood said.
