Richard Mondale yells at a Obama health care reform supporter during a protest in front of the U.S. Supreme Court building March 27, 2012, in Washington. / Getty Images
Updated at 4:28 p.m. ET
(AP) WASHINGTON - Sharp questioning by the Supreme Court's conservative justices cast serious doubt Tuesday on the survival of the individual insurance requirement at the heart of President Obama's historic health care overhaul.
Arguments at the high court focused on whether the mandate for virtually every American to have insurance "is a step beyond what our cases allow," in the words of Justice Anthony Kennedy.
But Kennedy, who is often the swing vote on cases that divide the justices along ideological lines, also said he recognized the magnitude of the nation's health care problem and seemed to suggest that it would require a comprehensive solution.
He and Chief Justice John Roberts emerged as the seemingly pivotal votes in the court's decision, due in June in the midst of a presidential election campaign that has focused in part on the new law. Republican candidates are strongly opposed.
Justices Antonin Scalia and Samuel Alito appeared likely to join with Justice Clarence Thomas to vote to strike down the key provision of the overhaul. The four Democratic appointees seemed ready to vote to uphold it.
The congressional requirement to buy health care insurance is the linchpin of the law's aim to get medical insurance to an additional 30 million people, at a reasonable cost to private insurers and state governments. Virtually every American will be affected by the court's decision on the law's constitutionality.
The biggest issue, to which the justices returned repeatedly during two hours of arguments in a packed courtroom, was whether the government can force people to buy insurance. And if so, could other mandates to buy broccoli, burial insurance and cellphones, for example be far behind?
"Purchase insurance in this case, something else in the next case," Roberts said.
"If the government can do this, what else can it not do?" Scalia asked.
Kennedy at one point said that allowing the government mandate would "change the relationship" between the government and U.S. citizens.
"Do you not have a heavy burden of justification to show authorization under the Constitution" for the individual mandate? asked Kennedy.
At another point, however, he also acknowledged the complexity of resolving the issue of paying for America's health care needs.
"I think it is true that if most questions in life are matters of degree ... the young person who is uninsured is uniquely proximately very close to affecting the rates of insurance and the costs of providing medical care in a way that is not true in other industries. That's my concern in the case," Kennedy said.
Roberts also spoke about the uniqueness of health care, which almost everyone uses at some point. "Everybody is in this market, so that makes it very different than the market for cars or the other hypotheticals that you came up with, and all they're regulating is how you pay for it," Roberts said, paraphrasing the government's argument.
Solicitor General Donald Verrilli Jr. sought to assure the court that the insurance mandate in the Patient Protection and Affordable Care Act that Mr. Obama signed into law two years ago is a key part of the law's goal of reaching many of the more than 40 million people who don't have health insurance through their employers, don't qualify for government aid and cannot afford to buy coverage on their own.
Indeed, the law envisions that insurers will be able to accommodate older and sicker people without facing financial ruin because the insurance requirement will provide insurance companies with more premiums from healthy people to cover their increased costs of care
Paul Clement, a predecessor of Verrilli's who is representing Florida and 25 other states in challenging the law, called the mandate "an unprecedented effort by Congress."
He said the requirement would force people, especially those who are young and healthy, to buy a product they don't want.
Justice Ruth Bader Ginsburg said she found the debate over health care similar to an earlier age's debate about the Social Security retirement system. How could Congress be able to compel younger workers to contribute to Social Security, but be limited in its ability to address health care? she wondered.
Does it to have to be "a government takeover"? she asked.
Clement acknowledged that a system of national health insurance might well be constitutional.
Earlier, Scalia repeatedly pointed out that the federal government's powers are limited by the Constitution, with the rest left to the states and the people. "The argument there is that the people were left to decide whether to buy health insurance," Scalia said.
Scalia and Roberts noted that the health care overhaul law would make people get insurance for things they may not need, like heart transplants or pregnancy services. "You can't say that everybody is going to participate in substance abuse services," Roberts said.