Underscoring the challenge President-elect Donald Trump faces repealing the Affordable Care Act, more than 100,000 people signed up for health coverage through the law on Wednesday, the day after Trump's election.
The tally, reported Thursday by the Obama administration, marked the busiest day since the enrollment period for coverage in 2017 began Nov. 1.
"Best day yet this open enrollment," Health and Human Services Secretary Sylvia M. Burwell tweeted.
The enrollment period, the fourth since the law's coverage expansion began, comes at a critical moment for the marketplaces and the health law that President Obama signed in 2010.
The coverage expansion has recorded historic gains over the last three years, as some 20 million previously uninsured Americans gained health insurance and the nation's uninsured rate dropped to the lowest level ever recorded.
Trump and congressional Republicans have pledged to repeal the law quickly after Trump takes office in January.
But the GOP has not to date advanced any alternatives that would protect the millions of people who now depend on health coverage through the law.
Many of these Americans have low incomes and rely on Medicaid, which has been expanded through the health law.
But about 11 million get commercial health plans through HealthCare.gov and similar state-based insurance marketplaces such as Covered California that were created through the law.
And more than 80% of these consumers receive government subsidies to offset the cost of their premiums.