The man often known as the Supreme Court's swing justice posed tough questions about the scope of the controversial health care overhaul Tuesday, suggesting he might have doubts about its validity.
Justice Anthony Kennedy did not fully tip his hand as to how he might ultimately vote in the case -- leaving all sides to ruminate for the next few months until an expected summer ruling.
On this most important day of arguments for the landmark case, most of the high court bench was thoroughly engaged for a two-hour debate over the constitutional merits of President Obama's health care law. Based on the tenor of Tuesday's arguments, the justices appeared to be closely divided and this case, as do so many other close ones at the high court, may ultimately come down to Kennedy's vote.
Early in the arguments, the veteran justice cut to the heart of the debate over the so-called individual mandate -- which was the focus of Tuesday's hearing -- asking the federal government's attorney to explain what constitutional power the government had to force all Americans to obtain health insurance.
"Can you create commerce to regulate it?" Kennedy asked Solicitor General Don Verrilli.
That question addressed the key issue about whether Congress exceeded its regulatory authority under the Commerce Clause, which gives the federal government the power to pass laws governing economic activity among the states. Verrilli said that's not happening with the mandate; rather it is a regulation of a pre-existing health care marketplace.
Later, Kennedy described the law as unique and said the mandate "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."
He acknowledged the Court normally gives Congress the benefit of the doubt on laws that it passes, but in this instance there was a "heavy burden of justification" necessary for supporters of ObamaCare to prove its legal worth. He also wondered about what limits to federal power would be in place if the court signed off on law.
What's not clear is if the answers provided by Verrilli about the narrowness of the law, or much else, satisfied Kennedy's apparent doubts.
The comments and questions from the other justices generally suggested they would fall along familiar ideological divisions. If that ultimately happens, it will be a 5-4 decision on this fundamental issue that will determine the law's fate.
At the start of his arguments, repeatedly interrupted by a scratchy throat, Verrilli plainly stated that "the Affordable Care Act addresses a fundamental and enduring problem in our health care system and our economy." That problem the ACA attempts to fix is the ability of insurance companies to drop or deny coverage based on preexisting medical conditions or other reasons.
The government's fix involved a requirement that all Americans obtain health insurance. This solved two problems for lawmakers. It would lead to health coverage for all people-a major issue for the president's base -- and it also covers the increased insurance costs by forcing these newly insured people, including many healthy people with minimal health care needs, into the system.
"So the mandate is forcing these people to provide a huge subsidy to the insurance companies for other purposes that the act wishes to serve," Justice Samuel Alito said.
But Justice Ruth Bader Ginsburg likened the ACA to the Social Security Act, which the Court ruled constitutional, as an example of where younger healthy people cover the payouts for older and infirm Americans.
In this context, she offered a simple explanation for that practice: "If you're going to have insurance, that's how insurance works."
It's also an area that Justice Elena Kagan touched upon. "And this is especially true, isn't it, General Verrilli, because in this context, the subsidizers eventually become the subsidized?" she asked.
Verrilli agreed, saying people never know when they'll need coverage.
It was an answer Justice Antonin Scalia jumped on.
"We're not stupid. They're going to buy insurance later. They're young and need the money now. When they think they have a substantial risk of incurring high medical bills, they'll buy insurance, like the rest of us," he said.
Unlike Scalia and Alito who were more animated with their comments expressing doubt about the law's validity, Chief Justice John Roberts plainly offered some of his own concerns that at times mirrored Kennedy's.
He used the phrase "all bets are off" twice when talking about the ways future Congresses will attempt to fix perceived problems if the law survives. "There's this health care market.
Everybody's in it. So we can regulate it, and we're going to look at a particular serious problem, which is how people pay for it. But next year, they can decide everybody's in this market, we're going to look at a different problem now, and this is how we're going to regulate it. And we can compel people to do things -- purchase insurance, in this case. Something else in the next case, because you've -- we've accepted the argument that this is a market in which everybody participates."
Some of the justices wondered whether the government could compel people to exercise, eat broccoli or buy certain cars if the mandate is upheld. Verrilli maintained that wouldn't be the case.
"The (health insurance) market is regulated at the federal level in very significant ways already," Verrilli told the chief justice. "The question is, is there a limit to the authority that we're advocating here under the commerce power, and the answer is yes, because we are not advocating for a power that would allow Congress to compel purchases."
The government's defense of the ACA also relied upon the Constitution's Necessary and Proper Clause and taxing power. Those issues did briefly come up during the two-hour long arguments but were very much overshadowed by the debate over the mandate's relationship to federal authority in regulating commerce.
Justice Clarence Thomas, as is his custom, did not speak in the courtroom. But his views on the expansion of the Commerce Clause have been clearly articulated in past cases where he objected to increased federal power. Based on those writings, it is widely assumed that he will similarly object to the scheme presented here.
Lawyers for the 26 states opposed to ObamaCare and the National Federation of Independent Businesses also faced tough questions from the justices. But by the time each took the lectern in the second hour of arguments, the Court's direction seemed clear.
For the second day in a row, Attorney General Eric Holder and Health and Human Services Secretary Kathleen Sebelius were in the courtroom. A number of prominent lawmakers from Capitol Hill were also in attendance. Sen. Patrick Leahy, D-Vt., chairman of the Senate Judiciary Committee and major supporter of the law, looked concerned over the questions Kennedy asked.
Wednesday's final day of arguments will be split into two sessions. The first will examine whether the rest of the ACA is severable from the individual mandate if the high court strikes down that provision. The last case looks at the law's provision to expand Medicaid coverage. The challenging states call that part of the law coercive.
Fox News' Shannon Bream contributed to this report.