President Obama addresses the public using Facebook Live. He encouraged people to enroll in health-care plans under the Affordable Care Act. (White House)

President Obama on Friday urged the American public to press the Republican-led Congress not to abandon gains in insurance coverage and access to health care that the Affordable Care Act has brought during the past six years.

The president’s brief remarks, on Facebook Live in front of a White House fireplace with Christmas decorations, were his most pointed since last month’s election about the fate of the health-care law that stands as the largest domestic achievement of his presidency — and a main target of President-elect Donald Trump and the Republican majority in Congress.

Obama spoke amid the fourth year’s enrollment period for consumers to buy health plans through ACA marketplaces, created for people who cannot get affordable coverage through a job. “If you haven’t gotten covered, now is the time to do it,” the president said, noting that Dec. 15 is the deadline for people to have insurance at the start of 2017.

Trump has said that abolishing the ACA will be one of his first priorities. This week, he chose as his health secretary a vehement critic of the law. Obama administration officials have contended that a strong enrollment would demonstrate support for the law and act as a buffer against its repeal.

“Don’t let Republicans in Congress” take away the ACA’s most popular features, Obama said. “Tell them, ‘We want to build on the progress we’ve made, not abandon it.’ ”

On Wednesday, federal health officials announced that, during the first four weeks of the three-month enrollment period, 2.1 million people have selected plans through HealthCare.gov, the ACA’s federal insurance exchange, slightly ahead of a year ago.