WASHINGTON — The Supreme Court sent a clear message Thursday that President Barack Obama’s health care overhaul is here to stay, rejecting a major challenge that would have imperiled the landmark law and health insurance for millions of Americans.

Whether you call it the Affordable Care Act, Obama- Care, or in the words of a dissenting justice, SCOTUScare, Obama’s signature domestic achievement is, as the president himself put it, “reality.”

The 6-3 ruling, which upheld financial aid to millions of low- and middle-income Americans to help pay for insurance premiums regardless of where they live, was the second major victory in three years for Obama in politically charged Supreme Court tests of the law.

And it came on the same day the court gave him an unexpected victory on another subject, preserving a key tool the administration uses to fight housing bias.

Obama greeted news of the health care decision by declaring the law is no longer about politics but the benefits millions of people are receiving. “This is no longer about a law,” he said in the White House Rose Garden. “This is health care in America.”

Declining to concede, House Speaker John Boehner of Ohio said Republicans, who have voted more than 50 times to undo the law, will “continue our efforts to repeal the law and replace it with patient-centered solutions that meet the needs of seniors, small business owners and middle-class families.”

However, he declined to commit to a vote this year.

Several Republican presidential candidates said they would continue the fight, ensuring it will be an issue in the campaign.

Other legal challenges are working their way through the courts, but they appear to pose lesser threats to the law, which passed Congress without a single Republican vote in 2010 and has now withstood two stern challenges at the Supreme Court.

At the court, Chief Justice John Roberts again wrote the opinion in support of the law, just as he did in 2012. His four liberal colleagues were with him three years ago and again on Thursday. Justice Anthony Kennedy, a dissenter in 2012, was part of the majority this time.

Roberts said to read the law the way challengers wanted would lead to a “calamitous result” Congress could not have intended.

“Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them,” Roberts declared.

Justice Antonin Scalia, in a dissent he summarized from the bench, strongly disagreed.

“We should start calling this law SCOTUScare,” he said, using an acronym for the Supreme Court and suggesting his colleagues’ ownership of the law by virtue of their twice stepping in to save it from what he considered worthy challenges.

His comment drew a smile from Roberts, his seatmate and the object of Scalia’s ire.