One of the hallmarks of Donald Trump's campaign was a promise to repeal the Affordable Care Act (ACA), a legislative milestone of Pres. Barack Obama's administration. Indeed, on his Web site Trump declared, “On day one of the Trump administration, we will ask Congress to immediately deliver a full repeal of Obamacare.” In his “Contract with the American voter” the president-elect vowed again to repeal the ACA within the first 100 days of his administration. There is no doubting his intentions.

Trump has also proposed several other controversial health-related measures, including defunding Planned Parenthood and reducing drug costs via drug importation. But which of these health-based initiatives will he actually be able to accomplish in the early days of his administration?

Since its enactment in 2010, Republicans have rallied several times to repeal the Affordable Care Act (ACA), which, as of today provides health insurance to some 20 million Americans. Now backed by a Republican-led Congress, Trump has vowed to permit states to sell health insurance across state lines to allow competition, dismantle Medicaid and turn it into a grant program administered by the states, and increase the accessibility of Health Savings Accounts.

Although Trump’s administration could make aspects of the ACA difficult for those trying to enroll, experts believe a full legislative repeal, requiring 60 Senate votes, on day one or even in the first 100 days, is unlikely, as Scientific American reported soon after his election. “A straight up and down repeal vote seems very difficult because most Congress[members], my guess is, would want to know what will replace it, and he's unlikely to have a replacement plan ready in the first 100 days—that takes time to develop,” says David Cutler, professor of applied economics at Harvard University and former senior health care advisor in the Obama administration. (The ACA was passed just over a year after Obama announced his intent to enact a national health care plan.) And there is always the possibility of a Democratic filibuster in the Senate—a tactic used to delay or block legislation.

Short of a full-on repeal, Trump and the Republicans could take measures to modify some aspects of the ACA. One is via a budget reconciliation process, which limits amendments to provisions in the law that have a substantial impact on the budget, and would allow Republicans to circumvent delays. “The reconciliation bill doesn't need to pass a filibuster, it just needs [51] votes, and the Republicans have more than that in the Senate,” Cutler says. “So they could get rid of not all, but some [ACA elements] through reconciliation.”

In principle, a reconciliation bill could pass in the first 100 days but experts believe it would be unlikely to happen that quickly without replacement legislation. “I can't imagine a full house and a third of the Senate wants to run in 2018 having withdrawn funding for expanded coverage without having anything in its place,” says Gail Wilensky, Senior Fellow at Project Hope and a former senior health and welfare adviser to Pres. George H. W. Bush. Republican “Sen. Wicker, from Mississippi, is already on record saying we're not going to leave 20 million people without coverage, which suggests they are going to do something to give themselves time.”

Items in the ACA that could not be changed during reconciliation include provisions such as reforms to the commercial insurance market, marketplace policies and consumer protection measures, explains Caitlin Morris, Health System Transformation program director at Families USA, a nonpartisan consumer health advocacy group.

Without a proper replacement plan in place, a repeal or substantial reconciliation bill will certainly be met with outrage from both the public and health advocacy organizations. “You've got to convince people that it’s a good idea to take health care away from middle- and low-income Americans and give tax cuts to high-income Americans,” Cutler says.

A more likely outcome, say experts, is that Congress could either delay passing the repeal or the members could pass a bill for the repeal but delay its implementation in order to buy time for developing a replacement. In the meantime the Trump administration could make aspects of the ACA difficult, in effect destabilizing an already vulnerable system. “He could screw up the implementation so much that he kicks off a lot of people,” Cutler says. “He could say we're going to develop fewer resources for signing people up and discourage people from enrolling. So he could do all those sorts of things administratively and [cause] a lot of damage without legislation.”

Part of Trump’s campaign trail promise has also been to restrict access to abortion through defunding Planned Parenthood. The organization receives just upward of $450 million a year in federal funding, according to the Congressional Budget Office—not a significant budgetary burden for the government (total government funding, including state and local dollars, totals approximately $553 million, according to a Planned Parenthood spokesperson). These dollars account for just under half of the nonprofit’s backing. The GOP could decide they want to cut Planned Parenthood’s funding right away. They, however, would still have to go through various legislative processes. “Generally speaking, as a matter of constitutional law, it is up to Congress how federal money is spent,” says David Law, a professor of constitutional law and political science at Washington University in Saint Louis. “If Congress wants to ensure Planned Parenthood gets money, it can do so regardless of what the president wants—because the president carries out the laws and can’t contradict the laws. Conversely, if Congress wants to strip Planned Parenthood of money, it can do so regardless of what the president wants.” Just last year Senate Republicans tried to defund Planned Parenthood, but the measure was blocked by Democrats. Republicans could propose a new budget as early as spring of 2017, which would have to be approved by the House and Senate.

Planned Parenthood funding aside, the Trump administration could restrict birth control access covered under the ACA, meaning insurance would no longer have to cover contraception. “The Department of Health and Human Services writes regulations about the law,” Cutler explains. “So they would write a new regulation, superseding the old regulation, stating contraception is no longer a covered service which you need to provide at no cost to women. And all [the president-elect] has to do is go through the normal rulemaking process, which involves putting out a proposal and getting comments and having them finalized. So he can do that without Congress saying so.” Rep. Tom Price (R–Ga.), an early Trump supporter, and a front-runner for secretary of Health and Human Services, would likely support such a decision. The Republican from Georgia has been an opponent of the ACA since its early days.

Other initiatives, such as Trump’s call for reduction in drug prices through increased drug importation would require legislation to pass, a process unlikely to occur in the first three months of his presidency. “While drug importation could provide relief in narrow situations, like a drug shortage, it will not provide immediate relief to consumers that struggle to afford high drug costs,” Morris says. “To protect consumers from rising prescription drug costs, we need a comprehensive set of reforms, including increased transparency surrounding drug companies’ pricing and practices, and alignment of prices with the value they provide to patients. That said, drug importation laws could be changed legislatively. It is possible, but unclear, if this could be done through the budget reconciliation process.”

In the end, the incoming administration will have to decide which issues deserve focus and which can be swiftly achieved. “Doing something dramatic about the ACA, such as being supportive of the financial repeal, with the implementation delayed, might be regarded as sufficient—so that’ll allow him to focus on energy, the economy, national security and maybe trade agreements,” Wilensky says. “I think he’s going to want to show that something has happened but I'm not sure how extensive that something has to be. It’s easier to take away than to redo. That’s the simple shorthand version.”