WASHINGTON -- On Day 3 of the Supreme Court's review of the U.S. health care overhaul, the justices are expected to ask lawyers in the case whether the law could survive even if its key mandate that Americans get medical insurance is struck down as unconstitutional.

President Barack Obama's administration has said the only other parts of the Affordable Care Act of 2010 that the court should kill if the individual mandate is abolished are changes requiring insurers to cover Americans with existing medical problems and limiting how much could be charged in premiums based on a person's age or health.

The administration, as demonstrated by skeptical questions Tuesday from the court's conservative justices about the legality of the individual mandate, must prove its case in the wake of the decision last August by the federal appeals court in Atlanta to strike down the requirement. The 11th U.S. Circuit Court of Appeals ruled, however, that the rest of the law can remain in place, a position that will be argued to the Supreme Court on Wednesday by a private lawyer appointed by the justices, H. Bartow Farr III.

During Wednesday's 90 minutes of argument, the nine justices are also expected to examine whether Congress has the power under the Constitution to require that states dramatically expand the Medicaid health care program for the poor. Expansion would make as many as 30 million more Americans eligible for Medicaid coverage.

The 26 states whose Republican attorneys general are suing to get the court to overturn the law, say forced expansion of Medicaid -- financed jointly by the federal government and states -- would violate the Constitution. Lower courts have ruled in the Obama administration's favor on this issue, explaining that states that object could leave Medicaid voluntarily.

On Tuesday, befitting his reputation as a swing vote on the ideologically divided high court, Justice Anthony Kennedy showed he could be the deciding vote on the health care law.

The questions Kennedy, nominated to the court by President Ronald Reagan, posed to lawyers arguing over the individual mandate revealed skepticism about the White House's justification for the Affordable Care Act.

At issue was whether the Constitution's Commerce Clause allows Congress to compel the purchase of medical insurance, so that a person is covered when he gets a costly or unexpected bill for health care services. Otherwise, the cost could be shifted to others throughout the country in the form of higher insurance-policy premiums.

Kennedy was seen as a potential vote to uphold the mandate, along with Chief Justice John Roberts, who usually votes with the court's conservative wing.

White House lawyers tried to appeal to conservative Justice Antonin Scalia, but that approach could fall flat if Tuesday's oral arguments were an indication.

But if Roberts holds true to past cases and follows Scalia, Kennedy will be the deciding vote that determines if Congress acted within its broad authority under the Commerce Clause.

During Tuesday's session, Kennedy characterized the health care law as one that institutes a fundamental change in the relationship between Americans and their government.

Do you not have a heavy burden to show authorization under the Constitution? he asked Solicitor General Donald Verrilli, the administration's Supreme Court lawyer.

Verrilli argued that the mandate regulates the ways Americans pay for health care. Congress, he said, wouldn't be able to force someone to buy insurance -- or any good or service -- as a means of stimulating the nation's economy.

But why not? Kennedy probed. If Congress says that the interstate commerce is affected, isn't, according to your view, that the end of the analysis?

Despite his and other justices' tough questions, Kennedy seemed to acknowledge the problem uninsured Americans pose to the health care system. He asked lawyer Paul Clement, representing the 26 states challenging the Affordable Care Act, whether the refusal of some individuals to join the market by buying insurance would put them outside the scope of regulation.

But they are in the market and in a sense they are creating a risk that the market must account for, Kennedy said.