THIS IS A precarious moment for President Obama. His poll ratings have slipped, and health-care reform, his most significant accomplishment, is in danger. In a White House news conference Thursday, Mr. Obama forthrightly accepted blame and offered two ways to repair the damage. One is crucial. The other is misguided.

“We fumbled the rollout of this health-care law,” the president declared. He admitted that he was wrong to have pledged that those who liked their insurance plans could keep them, and he took responsibility for misleading representations that other Democrats made based on his promises. He rightly said he would have to earn confidence back by making the Affordable Care Act work.

That will require fixing the Web site. was supposed to be the public’s primary interface with a reorganized insurance industry, where millions would shop for coverage, view bottom-line prices and enroll in plans easily. Phone and mail-in enrollment options can augment but cannot substitute. Reform depends on healthy people signing up and paying into the system. As the president signaled, the administration must get the site right.

Mr. Obama’s big announcement Thursday, though, was a “fix” to the Affordable Care Act meant to redeem his promise that “if you like your health-care plan, you can keep it.” Unfortunately, it was his promise that was wrong, not the design of the law. At best, his proposed fix will have little impact except to let him shift the blame; at worst, it will undermine reform.

The president offered relief to the sliver of Americans whose policies were canceled in recent weeks. Though their plans did not comply with the quality standards properly set by the law, and though many of them will be due generous subsidies to buy better plans next year, some of the affected people were going to have to pay more in the new system. Anger and confusion over these cancellations became a problem for the Democrats. So Mr. Obama said the government will allow insurance companies to offer non-compliant plans to current customers for another year.

That doesn’t mean everyone affected will be able to keep his policy. Some state governments will say no. Some insurance companies will be unable or unwilling to execute a U-turn at this late date , even if state regulators let them try. The president’s fix, then, would merely ease the pressure Democrats are feeling and shift blame onto state and insurance-company officials.

That would be a better outcome, though, than if companies take full advantage of Mr. Obama’s new policy and extend many plans that were set to end, draining the new system of enrollees it needs to function well. Insurers who decided to act would try to hold onto their healthiest customers — those who don’t make many claims, if any. But the Obamacare marketplaces need those relatively healthy customers. If the system struggles in its opening years, the pressure to pull the plug will only grow. This outcome is unlikely, but anything that poses a threat to the integrity of the system’s risk balancing rightly worries health-care policy experts.

The chief — the only — advantage of Mr. Obama’s proposal is that it’s not as bad as the “fixes” being floated by panicked Democrats and gloating Republicans in Congress.