The Affordable Care Act requires uninsured Americans to purchase health insurance beginning in 2014 or face a penalty, likely on their federal income tax. Opponents claim that the so-called "individual mandate" is unconstitutional. The Obama administration says the mandate falls well within the scope of congressional power to regulate interstate commerce and impose taxes.
"There were many justices who were expressing great skepticism about the mandate's constitutionality, and given precedent and prior case law, the degree of their skepticism was perhaps somewhat surprising but not shocking," says Wendy Parmet, professor of law at Northeastern University.
Chief Justice John Roberts and Justice Antonin Scalia, two of the court's conservatives, hammered Solicitor General Donald Verrilli on whether the individual mandate sets a dangerous precedent.
"It's good for you in this case to say, 'Oh, it's just insurance,'" said Roberts. "But once we say that there is a market and Congress can require people to participate in it ... it seems to me that we can't say there are limitations on what Congress can do under its commerce power."
Verrilli maintained that health care, by virtue of "the unique nature of this market," is not working like other free markets. Instead, he said the system is transferring "many billions of dollars of uncompensated costs" to other market participants, resulting in higher premiums for the insured and making health coverage too expensive for more than 30 million uninsured Americans.
With the court seemingly split along ideological lines, attention was focused on swing-vote Justice Anthony Kennedy. True to his traditional tiebreaker role, Kennedy seemed to side with conservatives early on but ended the session by noting that the uninsured, by their nonparticipation, have a significant impact on the health care market.
Legal observers see close ruling
Will mandatory health insurance survive the crucible?
"I wish it had gone better ... but I don't think it's hopeless," says Tim Jost, health law scholar and professor of law at Washington and Lee University. "I think the press probably read a bit too much into the extent to which Justice Kennedy was pressing the solicitor general and the plaintiffs. I still think it's likely that the statute will be upheld, but it was a lot closer than I expected it to be."
Parmet agrees: "I think it's too close to call. I would not be surprised with a 5-4 or 6-3 decision going either way."