Donald Trump has promised to repeal one of President Barack Obama's signature programs as soon as he takes office. So what could that mean for people depending on the Affordable Care Act? 

Donald Trump has been clear about his plans to repeal the Affordable Care Act and has said he plans to convene a special session of Congress to do just that.

It is now more likely than ever that could happen, with both the House and U.S. Senate in Republican control. But it's much more complex than a simple vote.

Not only would a repeal affect the 20 million Americans who are enrolled in marketplace plans, but it would also reverse some key provisions that everyone benefits from, including preventing insurance companies from denying coverage to those with pre-existing illnesses.

"Certainly, there's a lot of public support for insurance regulation and the protection of patients," said Miriam Laugesen, associate professor of health policy and management at the Columbia Mailman School of Public Health. "Not everything in the ACA is likely to be repealed just because they are popular policies." 

Experts say it would be a heavy lift now to turn the industry in a different direction. Still, changes are expected, but Trump has supplied few details, so it's hard to say what the impact would be.

One thing we've heard him say is that he would like to allow competition of insurance plans across state lines, which Obamacare already allows for. But that would be very difficult to do, because every state has its own policies. 

New York, in particular, has been known for more generous health policies with stricter insurance regulation.

"If the state government has a role, I think there's going to be a bit of continuity with that," Laugesen said. "It just depends. If it's a federal program and it's cut, that puts states in a difficult position. But certainly, states often step in when the federal government is pulling back."

In the meantime, Democrats have enough votes to exercise their filibuster option in the Senate to hold off the repeal process if it progresses quickly to a vote.