Key justices signal their support for health care law.

WASHINGTON — The bulk of the Affordable Care Act, the sprawling 2010 health care law that is President Barack Obama’s defining domestic legacy, appeared likely to survive its latest encounter with the Supreme Court in arguments Tuesday.

It was not clear whether the court would strike down the socalled individual mandate, which was rendered toothless in 2017 after Congress zeroed out the penalty for failing to obtain insurance.

But at least five justices, including two members of the court’s conservative majority, indicated that they were not inclined to strike down the balance of the law. In legal terms, they said the mandate was severable from the rest of the law.

“It does seem fairly clear that the proper remedy would be to sever the mandate provision and leave the rest of the law in place,” said Justice Brett Kavanaugh.

Chief Justice John Roberts made a similar point.

“Congress left the rest of the law intact when it lowered the penalty to zero,” he said.

Tens of millions of Americans gained insurance coverage under the 2010 law, which includes popular provisions on guaranteed coverage for preexisting medical conditions, emergency care, prescription drugs and maternity care. Republican state officials, backed by the Trump administration, say that a key provision of the law is unconstitutional, and that this means the whole law must fall.

The law has survived two earlier challenges in the Supreme Court.

Since the last major challenge, three new justices have joined the court, all appointed by President Trump. One of them, Justice Amy Coney Barrett, has been publicly critical of the earlier rulings.

The new case, California v. Texas, No. 19840, was brought by Republican officials who said the mandate became unconstitutional after Congress in 2017 zeroed out the penalty for failing to obtain health insurance because it could no longer be justified as a tax.

They went on to argue that the mandate was a crucial feature of the law, meaning that every other part of it should be wiped out.

The challenge has largely succeeded in the lower courts.

Democratic states and the House asked the Supreme Court to intervene, saying a prompt decision was needed to remove the uncertainty caused by the lower courts’ decisions.