(Bloomberg) —Key Republicans in Congress are cautioning that replacing Obamacare will be a difficult and lengthy process that won’t happen in the first days of President-elect Donald Trump’s administration.

U.S. Senator Lamar Alexander, chairman of the Health, Education, Labor and Pensions Committee, said the health-care law should be replaced in a “step-by-step” process to give states more control, which won’t be done quickly.

“I imagine this will take several years to completely make this transition,” Alexander, a Republican from Tennessee, told reporters in Washington Thursday. “We need to gradually move those decisions back to states and to individuals and do it in a way that does no harm to people today.”

The 2010 Affordable Care Act, as Obamacare is also known, took years to legislate and implement. Trump and Republicans have said they want to keep some parts of the law, like popular provisions guaranteeing coverage. They have yet to settle on other matters, though, like whether or how much financial support to give people. A repeal signed in Trump’s first days might not take effect right away — giving Republicans a lengthy period to try and write complex policy and avoid a sudden shock to the health-care system.

Repeal is the simple part, said Senate Finance Committee Chairman Orrin Hatch, a Utah Republican and key player in the health debate. Finding a replacement is harder.

“It’s not going to be an easy process, but I think Democrats and Republicans will work together to get a better system,” Hatch said to reporters in Washington on Wednesday.

Repeal and Wait?

“It’s going to be harder than a lot of us think,” said Senator Lindsey Graham, a South Carolina Republican who opposed Trump’s run for president and has called for Obamacare’s repeal and replacement.

Whatever Republicans decide on may take years to implement. When a Republican-written repeal bill was sent to President Barack Obama in January, and vetoed, it included a two-year delay before kicking in. House Ways and Means Committee Chairman Kevin Brady, a Republican from Texas, said discussions are ongoing on repeal and replace, including on the idea of a built-in delay and what else would be in a bill.

“The answer is to be determined,” Brady told reporters this week.

Health insurers are waiting to see what Republicans propose, and urging Trump and the Republican Congress not to disrupt the health-care system further.

“At the moment, our message is, ‘Let’s be thoughtful,’” said Ceci Connolly, chief executive officer of the Alliance of Community Health Plans, which lobbies on behalf of regional and state-based insurers. “Let’s not disrupt millions of people.”

Popular Provisions

Republicans could keep those provisions they favor, like guaranteeing coverage for pre-existing conditions, and eliminate one they strongly oppose, the “individual mandate” — a requirement that all Americans purchase health coverage or face a financial penalty.

Yet without a mandate, they would need to find a way to convince a broad group of Americans to buy coverage, helping spread the risk for insurers. Conservatives in Congress and around Washington have put forth several alternatives.

Speaker of the House Paul Ryan has previously proposed tax incentives to help people buy coverage, similar to Obamacare, as well as protection from rising rates linked to illness for those who maintain continuous insurance coverage.

Record Lows

Under Obamacare, while the U.S. has reached a near record low number of uninsured, the law has had troubles. Large insurance companies, including UnitedHealth Group Inc. and Aetna Inc., have pulled back from selling coverage. Premiums are rising rapidly. And because many plans feature high deductibles, a Commonwealth Fund study this year found that about four in 10 adults in ACA plans aren’t confident they could afford care if they got sick.

Still, more than 1 million people selected insurance plans through Obamacare in the first two week of sign-ups this month, the U.S. said in a report Wednesday. More than 246,000 of those were new consumers.

“I think Trump has the idea that things move very quickly in his world, but his world is very different than the political world,” said Behrends Foster, a partner at Bluestone Strategies who previously worked for the health insurance lobby.

Democrats are likely to oppose the repeal bill, forcing Republicans to use a procedural move to speed the process. Then, both parties will have to dig in and legislate policies that could replace the parts of Obamacare that were eliminated. That won’t happen on Trump’s first day, said Joseph Antos, a scholar at the American Enterprise Institute, a conservative think tank in Washington that’s been a repository of Republican-favored health policies.

“What we’re going to see is a very long, typical Washington process,” Antos said.

–With assistance from Steven T. Dennis, Laura Litvan and Erik Wasson. To contact the reporter on this story: Anna Edney in Washington at aedney@bloomberg.net To contact the editors responsible for this story: Drew Armstrong at darmstrong17@bloomberg.net Stephen West, Cecile Daurat