Writing in yesterday's Washington Post, Georgetown law professor Randy Barnett surveyed the various legal challenges that the health care bill is likely to face. Here's his take on the constitutionality of the individual mandate under the Commerce Clause, which may be the strongest of the various challenges:
[T]he Supreme Court has long allowed Congress to regulate and prohibit all sorts of "economic" activities that are not, strictly speaking, commerce. The key is that those activities substantially affect interstate commerce, and that's how the court would probably view the regulation of health insurance.
But the individual mandate extends the commerce clause's power beyond economic activity, to economic inactivity. That is unprecedented. While Congress has used its taxing power to fund Social Security and Medicare, never before has it used its commerce power to mandate that an individual person engage in an economic transaction with a private company. Regulating the auto industry or paying "cash for clunkers" is one thing; making everyone buy a Chevy is quite another. Even during World War II, the federal government did not mandate that individual citizens purchase war bonds.
If you choose to drive a car, then maybe you can be made to buy insurance against the possibility of inflicting harm on others. But making you buy insurance merely because you are alive is a claim of power from which many Americans instinctively shrink. Senate Republicans made this objection, and it was defeated on a party-line vote, but it will return.