There is no doubt that a state can constitutionally require citizens to have health insurance. Why, then, is the Supreme Court fussing over the constitutionality of the individual mandate provision of the Affordable Care Act?

The answer is simple. States have plenary authority to legislate on matters of public policy. The national government, however, is a government of limited powers. It cannot constitutionally act unless the Constitution authorizes it to do so. The central question in the case now pending before the Supreme Court is whether the Constitution grants Congress the authority to require individuals to have health insurance. Opponents of the law argue that it exceeds the legitimate authority of the national government.

The government defends the constitutionality of the individual mandate on the basis of the Commerce Clause of the Constitution, which provides in Article I, Section 8, that Congress shall have the power "to regulate Commerce ... among the several States."

Over time, the Supreme Court has held that under this provision Congress can constitutionally regulate activity if, in the aggregate, it has "a substantial economic effect on interstate commerce." Moreover, as Justice Rehnquist explained in 1995, the Court's role in determining the constitutionality of federal legislation under the Commerce Clause is limited to deciding whether Congress "had a rational basis ... for concluding that a regulated activity sufficiently affected interstate commerce" to merit federal action.

It is the Commerce Clause that authorized Congress to enact such legislation as the Sherman Antitrust Act of 1890, the Fair Labor Standards Act of 1938, the Civil Rights Act of 1964, the Environmental Policy Act of 1969, the Controlled Substances Act of 1970, and the Americans with Disabilities Act of 1990, to cite just a few examples.

In light of past decisions of the Supreme Court, arguments against the constitutionality of the Affordable Care Act initially seemed completely spurious. There can be no doubt that the economic effects of the health care industry on interstate commerce are huge, comprising more than 17 percent of the entire national economy. Thus, whatever the merits of the individual mandate in terms of public policy, there seemed no serious question about its constitutionality.

But here we are, the day after the Supreme Court heard arguments on the constitutionality of the individual mandate, and commentators reading the tea leaves of the justices' questions think that there is now a realistic possibility that Justices Roberts, Scalia, Kennedy, Thomas and Alito might actually vote to hold the Act unconstitutional. This is surprising even to many conservatives, who might not like the Act, but who nonetheless think it is clearly constitutional.

What, then, is the argument against the constitutionality of the individual mandate? The argument, quite simply, is that unlike other federal regulations of economic activity, the individual mandate requires individuals to do something (buy health insurance) even though they have not affirmatively done anything themselves to affect commerce.

Read more at Huffington Post