HOUSE SPEAKER Paul D. Ryan (R-Wis.) told GOP donors Monday that he had not abandoned his effort to pass a major health-care reform bill. But he sounded a more realistic note last Friday: “We’re going to be living with Obamacare for the foreseeable future,” he admitted after House Republicans failed to unite around a repeal-and-replace bill.

The real question facing Republicans is one Mr. Ryan fielded Friday: “Do we try to prop it up?” His answer: “It is so fundamentally flawed, I don’t know if that is possible.”

Actually, it is possible, and it is the responsibility of Mr. Ryan, his GOP majority and President Trump. “Moving from an opposition party to a governing party comes with growing pains,” Mr. Ryan said. Indeed: A governing GOP would restrain its anti-Obamacare hyperbole and seek to ensure the system’s stability, because millions depend on it. Instead, Republicans still sound as though they are rooting for it to fail. “The best thing politically is to let Obamacare explode,” Mr. Trump said shortly after the repeal-and-replace bill went down. Mick Mulvaney, the president’s budget director, insisted Sunday that the system cannot be fixed and “must be removed.”

In fact, the Congressional Budget Office projected that, left to operate under reasonable management, Obamacare can work pretty well, preserving the massive coverage gains of the past several years. But one wrong move, motivated by either malice or ignorance, could send the system crashing down.

The Trump administration will face an early test in how it handles a lawsuit the House filed against the Obama administration, which the new president’s team inherited. If Congress refuses to back down or the Justice Department fails to continue fighting the suit, the result would be the loss of subsidies that help millions of low-income people pay out-of-pocket health costs. Withdrawing this support would cause insurers to flee Obamacare markets, leading to massive coverage losses. Cooperation between Congress and the White House could easily solve this problem, but Republicans would have to agree to bolster an element of a law they have for years hysterically condemned.

Similarly, Mr. Trump must decide how he will enforce the individual mandate, a policy hated on the right that requires every American to obtain health coverage. The administration sent early signals that it would weaken enforcement, which would result in fewer people signing up and strain the system’s financial stability. But if Obamacare will be in place for the “foreseeable future,” enforcing the mandate will be essential, assuming the president wants to avoid presiding over a policy disaster for which, make no mistake, he would be blamed.

The president and Congress have means to improve the system, possibly even with serious Democratic buy-in. In a USA Today op-ed, Andy Slavitt, a senior Obama administration health-care official, laid out several options. Health and Human Services Secretary Tom Price, for example, could smartly employ his power to allow states to experiment with the Obamacare model. One area of agreement could be on state reinsurance programs, which work in a way similar to one of the ideas Republicans included in their repeal-and-replace bill.

Also important will be competent day-to-day management. That includes working with insurers to set sensible rules for enrollment periods, making sure risk-sharing mechanisms are working well and restoring outreach efforts to encourage more people to sign up. This may not be the job Republicans wanted. But it is the one they have.