President-elect Donald Trump promised repeatedly during his campaign that, upon taking office, he would immediately "repeal and replace" Obamacare—one of his predecessor's signature legacies.

What might that look like?

Don Berwick, former Administrator of the Centers for Medicare and Medicaid, said that Trump's specific policy proposals have not been a central part of his platform. But he suspects the President-elect might rely on House Speaker Paul Ryan, whose plans for repealing Obamacare were passed by Congress but vetoed by President Obama earlier this year.

Here are some of the key ways Obamacare could change under Trump and Ryan's plans. 

1. Changing the way Medicaid is funded.

One of the key provisions of Ryan's plan that is also endorsed by Trump is to change the funding for Medicaid, a program that provides health insurance for low-income Americans.

"Right now in Medicaid, if your state has more poor people because there's a recession, the federal government will step in," Berwick explained. "It's what you might call counter-cyclical funding: when things are bad, the federal government helps more. When things are better, the federal government helps less."

Ryan's proposal would fund Medicaid through "block granting," meaning the federal government gives the states a fixed amount of money to spend as they see fit. But reduced funding and flexibility could force states to put more restrictions on who is eligible for health insurance and ultimately reduce the number of people who are covered. 

Under Obamacare, 15.7 million people were added to Medicaid, putting total enrollment at around 73 million people—about half of whom are children. 

2. Bringing back restrictions on preexisting conditions.

One of the most popular tenets of Obamacare is that insurers are not allowed to deny coverage to Americans who have preexisting conditions, like serious or long-term illnesses which increase the chances of needing care.  

Under Ryan's plan, insurance is guaranteed, but only if coverage is continuous—meaning that, if your insurance is provided by your employer and you lose your job, you may not be able to get coverage again.

"There would be people, because they have diabetes and are changing jobs and the care isn't continuous, who would lose coverage and not be able to get it back. They would be angry," Berwick said.

3. Increased negotiation of drug pricing.

Trump has said he wants Medicaid to be able to negotiate prices for prescription drugs with pharmaceutical companies and to allow Americans to purchase imported drugs from overseas, where prices are generally lower. That's a proposal that Berwick himself supports.

"Drug prices in other countries are far lower than here," Berwick said. "Drug companies claim it's because we're subsidizing innovation and high prices are research investments. That's not true. That's not where the money is going."

4.  Decreased access to women's health care, including birth control.

Under Obamacare, insurers are required to provide birth control with no copay as part of preventative care—a benefit that could disappear if the law is repealed.

In Massachusetts, many features of Obamacare would be preserved even if the federal law is repealed because of the state's 2006 health care reform under Mitt Romney (also known as Romneycare.) This is not one of them. Though insurance companies are required to cover birth control, it is not required that they provide it for free like it is under Obamacare.

Overall, Berwick notes, Obamacare has expanded health insurance access to over 20 million Americans, according to government statistics. That could make it politically difficult for Trump to repeal the law wholesale—a move that Berwick believes would be damaging for the country. 

"If the current stuff on the table were to happen, 22 million people would lose insurance in our country," Berwick said. "We would become less just than we were."

To hear more from Don Berwick, tune in to Boston Public Radio above.