REPUBLICAN LEADERS are beginning to sketch the agenda they will pursue next year, and top on their list is repealing Obamacare, a move they have promised for years. It seems to be dawning on them, however, that reality is more complicated than sloganeering. The GOP’s emerging plan is to vote immediately to repeal much of the Affordable Care Act but not have the repeal take effect for a few years, giving Congress time to deal with the complexities of crafting and passing a replacement.

This “repeal and delay” strategy may appear to be a reasonable way to minimize the negative effects of transitioning off Obamacare. It is not. The plan would represent a reckless act of congressional malpractice , threatening the well-being of millions of Americans. The threat of such a policy disaster down the road would have immediate and negative effects on the health insurance market.

Health-care experts and industry groups are sounding the alarm with increasing urgency. They worry, first, that Congress will schedule much of the law to expire in a few years and then fail to agree on a replacement. There is plenty of evidence that lawmakers would not be able to unite behind an alternative. Republicans already have spent years trying to agree on a preferred plan, without success. Meanwhile, strategies based on putting a metaphorical gun to Congress’s head generally fail to force action, as the “sequestration” gambit failed to produce bipartisan budget compromise.

The nonpartisan Urban Institute released a study Tuesday explaining that repeal without an eventual replacement would result in such a destructive unraveling of the individual insurance market that the health-care system would end up far worse off than before Obamacare, with some 30 million people losing coverage, uninsured rates spiking and strapped state governments facing massive new uncompensated health-care liabilities.

Even the possibility of anything like this outcome would terrify insurers participating in the Obamacare system now, as would uncertainty about the nature of a replacement if Congress managed to pass something. The American Academy of Actuaries sent a letter to congressional leaders Wednesday explaining that the uncertainty of repeal and delay would cause insurers to “reconsider their participation in the market and some may choose to exit in the near term.” That would cause “severe market disruption and loss of coverage.” Not in three years — now.

Repealing Obamacare is a bad idea. But even Obamacare opponents should commit to repeal only after passage of a credible replacement plan. Anything else would prove the trust Americans just placed in Republicans undeserved.