WASHINGTON — A federal appeals court on Wednesday struck down a central provision of the Affordable Care Act, ruling that the requirement that people have health insurance was unconstitutional.

But the appeals panel did not invalidate the rest of the law, instead sending the case back to a federal district judge in Texas to “conduct a more searching inquiry” into which of the law’s many parts could survive without the mandate.

The 2-1 decision, by a panel of the United States Court of Appeals for the Fifth Circuit in New Orleans, left the fate of the nearly decade-old health law in limbo even as access to health care has become a central issue in the presidential race. Republicans, for whom a decision to throw out the law heading into the presidential election year could have been a political nightmare, seemed relieved, while Democrats issued a flurry of statements emphasizing that the law was still in grave danger.