The New York City law in question -- which had banned the transportation of licensed, locked and unloaded handguns outside city limits -- was voluntarily rescinded last year and New York state later passed a new law mandating that no such restrictions ever be re-imposed.
The justices on Monday appeared narrowly divided on whether there is still a reason to get involved at the request of gun rights groups or dismiss the appeal altogether.
"What's left of this case?" Justice Ruth Bader Ginsburg asked Paul Clement, the attorney for gun rights groups challenging the law, asserting the first question at Monday's oral arguments.
"Petitioners have gotten all the relief they sought," she said, in her first public appearance on the bench since a health scare and hospitalization last month.
Justice Sonia Sotomayor was similarly skeptical.
"You're asking us to opine on a law that's not on the books anymore," Sotomayor told Clement.
"I don't think it's bad when people who have an argument settle their argument," interjected Justice Stephen Breyer.
The National Rifle Association and other pro-gun organizations, backed by the Trump administration, insist the argument is still very much alive. They want court to expand Second Amendment protections to explicitly include transport of lawfully possessed arms to a second home or gun range.