President Barack Obama threw down the gauntlet to Republican lawmakers hoping to repeal ObamaCare in his farewell address Tuesday night, challenging them to "put together a plan that is demonstrably better than the improvements we've made to our health care system."

"The uninsured rate has never, ever been lower. Health care costs are rising at the slowest rate in fifty years," Obama said in Chicago. "And if anyone can put together a plan ... that covers as many people at less cost - I will publicly support it."

Obama spoke came hours after President-elect Donald Trump pushed Congress to act swiftly to repeal Obama's signature domestic legislation, telling the New York Times that "Obamacare has been a catastrophic event."

"Long to me would be weeks," Trump said of the gap between repealing and replacing the law. "It won't be repeal and then two years later go in with another plan."

However, under the congressional timetable, procedural budget votes set for later this week in the House and Senate would put the repeal process in motion. But the vote on repealing "Obamacare" wasn't expected until mid-February at earliest; a full replacement hadn't been expected until months or even years later.

Amid the political maelstrom around the Affordable Care Act, millions of people are still signing up. The administration said Tuesday that 11.5 million enrolled nationwide through Dec. 24, ahead of the previous year's pace.

The Associated Press contributed to this report.