Obamacare Insurance Mandate Is Struck Down by Federal Appeals Court

“We look forward to the opportunity to further demonstrate that Congress made the individual mandate the centerpiece of Obamacare and the rest of the law cannot stand without it,” he said in a statement.

The Trump administration has yet to respond to the ruling. It took the highly unusual step of refusing to defend the law after the case was brought against the government early last year and sided with the plaintiffs — at first only partially, but after the lower court ruling invalidated the law, entirely.

That left the 21 intervening states, all with Democratic attorneys general, to appeal the lawsuit, joined by the House of Representatives after Democrats won control last fall. They maintained that the individual mandate remained constitutional, but even if the courts disagreed, they said, the rest of the law could remain.

Although the law has significantly reduced the ranks of the uninsured, it has not lived up to its promise for some groups who were supposed to benefit, particularly middle-class people who don’t get insurance through a job, earn too much to qualify for the premium subsidies the law provides and often struggle to afford coverage.

For now, the law stands and the government continues to enforce it. The Trump administration did not object and said it would continue to enforce the law until all appeals were exhausted.

Health care is playing a pivotal role in the Democratic presidential primary race, with some candidates calling for improving the Affordable Care Act, others aiming to replace it with a government-run system, but all planning to criticize Mr. Trump for supporting the lawsuit should they win their party’s nomination.

Abbe R. Gluck, a health care expert at Yale Law School who supports the health law, said she was heartened that the appeals panel “recognized some of the glaring weaknesses in the lower court opinion,” but frustrated that the law’s future would remain uncertain, and for now, in the hands of a lower-court judge who already tried to overturn it.