The future of America’s health care system could be decided by Anthony Kennedy, the Supreme Court justice from California who has become the court’s all-important swing vote.

Comments from the bench by the justices are not always a sign of how they will decide a case. But it was evident during Tuesday’s oral arguments on the federal Affordable Care Act that four liberal justices are inclined to find the law constitutional while four conservative jurists are very skeptical of the act’s mandate that nearly all individuals either have insurance or pay a financial penalty. Two of the conservatives == Justices Antonin Scalia and Samuel Alito — raised repeated questions about the mandate while Chief Justice John Roberts asked tough questions of both sides but appeared to more critical of the government. A fourth, Justice Clarence Thomas, asked no questions but is believed to be leaning against it.

That left Kennedy, who at first seemed to join the conservative side but later left just enough wiggle room in his position to leave some doubt about how he will come down.

Kennedy said that this law was different from any other because it would require Americans to buy a product — health insurance — rather than simply regulating the behavior of those who choose to enter that market. The law’s opponents claim that this is outside the scope of Congress’ power under the Constitution’s Commerce Clause.

“Can you create commerce,” Kennedy asked, “in order to regulate it?”

Solicitor General Donald Verrilli, arguing for the government, said Congress and the president were only regulating the health care market, not trying to create commerce.

“That’s not what is going on here, Justice Kennedy, and we are not seeking to defend the law on that basis,” he said.

But Kennedy came back to the same line of thinking later in the hearing.

“Here the government is saying that the federal government has a duty to tell an individual citizen that it must act,” Kennedy said, “and that is different from what we have in previous cases, and that changes the relationship of the federal government to the individual in the very fundamental way.”

Kennedy also said the government had a “heavy burden of justification” to show that it was authorized under the Constitution to require people to buy insurance. And he said that arguing that the health insurance market is unique might not be good enough, because “in the next case, (the government) will say that the next market is unique.”

Finally, though, near the end of the hearing, Kennedy gave the government’s side an opening. He said that “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 this case.”

Whether “uniquely proximately very close” is close enough for Kennedy will be the question that likely decides the future of this law.