Justice Anthony Kennedy's mixed queries left the most room for him to be seen as a possible swing vote to decide the issue. Chief Justice John Roberts also spoke up for both sides of the issue at times.
The four Democratic-appointed justices seemed to champion the law. If they all support it, at least one of the court's five Republican appointees would still be needed to uphold the law.
Two of them, Justices Antonin Scalia and Samuel Alito, sounded hostile, while a third, Justice Clarence Thomas, remained silent but is presumed likely to find it unconstitutional based on past opinions.
The two other Republican appointees may be the key. Roberts expressed skepticism that Congress has the power to require Americans to carry health insurance or pay a fine. But he also sometimes reiterated Obama administration arguments, leaving a murkier impression overall than the other conservatives.
Kennedy was hardest to read. He said the insurance mandate was "changing the relation of the individual to the government." Justifying that is a "heavy burden," he warned.
But Kennedy also indicated openness to the argument that the health insurance market is unique, so telling Americans they have to carry insurance isn't like forcing them to buy other products. Young people who forgo insurance — "that person who is sitting at home in his or her living room doing nothing" — are contributing to the price of others' coverage because they might require treatment and if they aren't insured, the costs of that treatment get passed on to other Americans in taxes and higher insurance premiums.
The court's liberals — Stephen Breyer, Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor — said little to shake expectations.
Of course, the questions might not mirror the justices' thinking, and their views could shift during the court's internal debates.
"It's foolhardy to try to predict the outcome of this decision based solely on the questions," said White House spokesman Josh Earnest.
Copyright 2012 The Associated Press.