Republican congressional leaders are coalescing around a plan to repeal Obamacare — and set up a deadline, two to four years in the future, to pass a replacement plan.

The idea, politically, makes sense. Republicans can quickly make good on their promise to repeal Obamacare and then get to the hard work of actually figuring out what should come next.

But here’s the problem: There would be huge real-world impact of merely enacting a repeal law, regardless of when the actual repeal takes effect. A successful repeal vote would tell insurers selling on Obamacare’s marketplaces to get out of the marketplace as soon as possible.

“Repeal and delay would be a terrible policy to adopt,” says former Congressional Budget Office Director Doug Elmendorf. “Passing it will badly damage the health care system. It would make far more sense to wait until the actual alternative is written.”

Outside analysts on both sides of the aisle warn that the approach could cause chaos. The legislative approach has splintered the Republican Party, with a handful of senators expressing opposition to repeal and delay — calling into question whether the approach could actually pass out of Congress.

“Insurers have got to put their products together this spring, and we’re right in the middle of killing Obamacare,” says Robert Laszewski, a longtime conservative health insurance consultant. “Are they going to submit proposals to sell in 2018? Why would they stay in the pool?”

Up until this week, repeal and delay looked like the Republicans’ best strategy for taking apart the Affordable Care Act — a way to deliver on a campaign promise while putting off the hard work of figuring out what comes next. But now that legislators are attempting to put the plan into action, the weaknesses are being laid bare — and demonstrating how difficult it will be for Republicans to end a program that provides insurance coverage to millions of Americans.

Why some Republicans think repeal and delay is a good strategy

Republicans have, for six years now, run campaigns where they promise to demolish the health care law and pass something else in its place. The problem is, Republicans gained control of Washington in the 2016 election — and the “something else” wasn’t quite ready.

Republicans do have a variety of Obamacare replacement plans that have been floating around Washington for some time (you can read my summary of the seven leading plans here). Most of those plans are still broad outlines that are just now getting picked up off the shelf. House Speaker Paul Ryan’s (R-WI) “Better Way” plan, for example, says that it will give Americans tax credits to help purchase insurance — but doesn’t say how big those tax credits will be. That is one of the many key details that Republicans still need to fill in as they craft a plan to replace the Affordable Care Act.

In early December, leading Republicans began to float the idea of repeal and delay. Senate Majority whip John Cornyn (R-TX) was one of the first, in a December 1 interview with Politico.

“We’re talking about a three-year transition now that we actually have a president who’s likely to sign the repeal into the law. People are being, understandably cautious, to make sure nobody’s dropped through the cracks,” he said.

Top Republicans began to make promises that nobody would lose coverage during this transition period, and that the Obamacare marketplaces would continue to function as they have for the past three years. People would still get the same tax credits to shop for coverage through Healthcare.gov or their local, state-based marketplace.

Ryan told USA Today that Republicans would aim to ensure that “no one is worse off” during this transition period. The problem is, health policy experts just don’t think that’s possible.

“Repeal and delay would be a terrible policy to adopt”

Obamacare’s marketplaces depend on private insurers showing up to sell coverage — and even before the threat of repeal, that was a struggle. The marketplace lost many plans this year as the people buying coverage turned out to be sicker and older than insurers initially expected.

Even before the election, Obamacare’s marketplaces were in a difficult place. There were serious discussions about whether they could retain enough insurers to continue to function properly, particularly in rural areas with small populations. Putting an expiration date on the marketplaces will only make insurers more reticent to stay in the market — and more likely to drop out.

Insurers need to make decisions far in advance about whether they’ll sell on the marketplaces. They will need to tell the Department of Health and Human Services this spring whether they plan to sell coverage in 2018. It is quite likely that, by this point, Obamacare will have been repealed without a replacement plan enacted.

So let’s say we’re in May 2017 and Republicans have indeed gone the repeal-and-delay route. They’ve passed a bill that ends Obamacare in January 2020 and are starting to debate replacement plans. Insurance executives can’t wait for legislators to delay repeal when they get close to the deadline — they need to decide this spring whether they want to sell on the Obamacare marketplaces.

Even before Donald Trump’s election, when Obamacare’s future seemed secure, the Obama administration sometimes struggled to get insurers on board. There have been multiple instances where no insurers wanted to sell in certain rural, low-population counties. The Obama administration had to swoop in at the last minute and convince at least one plan to sell.

Again, that was before Trump’s election. So think about what an undesirable business the marketplaces become when you’re given notice that the whole thing will shut down in two years.

“Without rapid action to stabilize the exchange markets, we are likely to see more insurers dropping out and another round of sharply increasing premiums,” Joe Antos and James Capretta, health policy experts at the conservative American Enterprise Institute, predict.

The half-dozen experts I’ve spoken with, from both sides of the aisle, roundly expect that repeal and delay would lead to some Americans losing insurance coverage during the delay period — either because premiums spike so high that they are unaffordable, or some areas of the country have no health insurers who want to sell plans.

“I expect the Congressional Budget Office will show a loss of coverage because of repeal and delay,” says Elmendorf, who now serves as dean of the Harvard Kennedy School of Government. He said it’s very difficult at this point to guess how large that loss of coverage would be, given how unprecedented this type of policy decision would be.

“CBO will have to apply a lot of judgment because we don’t have any clear, comparable situation in the past that I’m aware of,” Elmendorf says.

Some Republicans have become wary of the repeal-and-delay strategy — and that demonstrates the shifting politics of the Affordable Care Act

As experts began warning against the risks of repeal and delay, a handful of Republican senators have issued statements with similar concerns. This includes:

Sen. Lamar Alexander (R-TN) who was pressing party leadership in early December to do repeal and replace at the same time.

Sen. Rand Paul (R-KY) who wrote an op-ed on January 3 arguing against repeal and delay, and who was the sole Republican senator to vote against the initial step the Senate took Wednesday toward repeal.

Sen. Susan Collins (R-ME) who told a local newspaper she agrees with Sen. Alexander’s push to focus on replacement before repeal.

Sen. Bob Corker (R-TN) told reporters in December, “Why would we put off for three years doing what we know we have to do?”

We don’t know whether these senators will ultimately support repeal and delay or oppose it. But the reservations they are expressing are meaningful, and not all of them would have to follow through. Republicans need 50 votes plus Mike Pence’s tiebreaker to repeal Obamacare through the reconciliation process, and they have 52 seats in the Senate. Three votes against would be enough to sink the repeal process.

Obamacare was an easy target for campaign ads and stump speeches. But the reason you’re seeing intra-party Republican strife over repeal and delay is that legislators are now confronting what it will mean to disrupt the health coverage for millions of Americans.

They are looking at the expert warnings, about how repeal and delay wouldn’t just maintain the status quo in the marketplaces but could decimate them. And they’re seeing that repealing Obamacare, while maintaining the coverage that 20 million Americans have gained, is a whole lot harder than it looks.

Watch: Repealing Obamacare could change millions of lives