REPUBLICANS LIT the fuse on Obamacare Friday, approving the first step of the “reconciliation” procedure they can use to gut much of the law over even unified Democratic objections. Many Republicans are nervous. They should be: Millions of people’s lives are on the line, and the GOP has just set the country down a perilous path without a clear map showing where it will end up.

To encourage wavering Republicans, Speaker Paul D. Ryan (R-Wis.) argued on the House floor Friday that doing nothing was more dangerous than embarking down this uncertain road. “We have to step in before things get even worse,” he said. “This is nothing short of a rescue mission.” Mr. Ryan’s words mirrored those of President-elect Donald Trump, who insisted at a Wednesday news conference that the law is “imploding as we sit,” and who is urging Congress to pass both a repeal of Obamacare and a replacement within weeks.

“Misleading” would be a generous way to describe this spin. In fact, the Affordable Care Act has pushed the uninsured rate to historic lows; enrollment has held up this year; Obamacare markets are working well in a variety of states; in places where markets have been shakier, federal subsidies shield consumers from premium volatility; and the ACA Medicaid expansion continues to cover millions of people without trouble — save for that caused by Republicans who blocked the expansion in some states. If the ACA implodes in 2017, it will be due to presidential maladministration or Congress rushing through a sloppy repeal.

What issues the law has should be addressed through minor renovations. Republicans could strengthen provisions that encourage people to buy insurance or tighten rules that discourage people from signing up only when they are sick, for example. On top of an improved health-care system, the GOP could most likely get some Democratic votes for this approach. If Republicans went on to call that repeal and replace, more power to them.

Doing so would be significantly better than acting on the GOP’s more sweeping, previously proposed alternative plans, which aim to lower costs but would undermine the insurance pool, pushing out some of the neediest people in the process. In general, they would provide inadequate aid to help people buy insurance, encourage deductibles to rise, cut the benefits insurers must provide and enable insurers to discriminate more against the old and the sick. Not only would this sort of reform erode the current system, but also it would violate Mr. Trump’s own rhetoric, which criticizes the high deductibles that would become more prevalent under the previously articulated GOP reforms.

The fact that the policy discussion is still largely speculative while the repeal effort is on its way shows that Republicans have already begun legislating recklessly. Obamacare repeal should not have hit even the preliminary stage with so many details about the GOP’s vision for health-care reform glaringly absent. It would be all too easy for rushed reform to undermine the health-care system in disastrous ways. Republicans should slow down the process before it is too late.