In arguments scheduled for Tuesday, the Supreme Court will hear its third major fight over the 10-year-old law, popularly known as “Obamacare.” Republican attorneys general in 18 states and the administration want the whole law to be struck down, which would threaten coverage for more than 23 million people.

It would wipe away protections for people with preexisting medical conditions, subsidized insurance premiums that make coverage affordable for millions of Americans and an expansion of the Medicaid program that is available to low-income people in most states.

California is leading a group of Democratic-controlled states that is urging the court to leave the law in place.

The case comes to a court that now has three justices appointed by President Donald Trump: Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett, who joined the court late last month following her hurried nomination and confirmation to replace the late Justice Ruth Bader Ginsburg.

The three Trump appointees have never ruled on the substance of the health care law. Barrett, though, has been critical of the court’s earlier major health care decisions sustaining the law, both written by Chief Justice John Roberts.

The Supreme Court could have heard the case before the election, but set arguments for a week after. The timing could add a wrinkle to the case since President-elect Joe Biden strongly supports the health care law.

The case turns on a change made by the Republican-controlled Congress in 2017 that reduced the penalty for not having health insurance to zero. Without the penalty, the law’s mandate to have health insurance is unconstitutional, the GOP-led states argue.

If the mandate goes, they say, the rest of the law should go with it because the mandate was central to the law’s passage.

But enrollment in the law’s insurance markets stayed relatively stable at more than 11 million people, even after the effective date of the penalty’s elimination in 2019. According to the nonpartisan Kaiser Family Foundation, enrollment dropped by about 300,000 people from 2018 to 2019. Kaiser estimates 11.4 million people have coverage this year.

Another 12 million people have coverage through the law’s Medicaid expansion.

The legal argument could well turn on the legal doctrine of severability, the idea that the court can excise a problematic provision from a law and allow the rest of it to remain in force. The justices have done just that in other rulings in recent years.

But in the first big ACA case in 2012, Justices Samuel Alito and Clarence Thomas voted to strike down the whole law. Roberts and Justices Stephen Breyer, Elena Kagan and Sonia Sotomayor have voted to uphold it.

A limited ruling would have little real-world consequences. The case could also be rendered irrelevant if the new Congress were to restore a modest penalty for not buying health insurance.

A decision is expected by late spring.