Much ink has been spilled and many pixels activated in discussing the Obamacare* lawsuits, which at their outset were called legally frivolous political stunts. Having won several victories — most importantly in the 26-state suit before the Eleventh Circuit Court of Appeals — these constitutional challenges, now recognized as quite serious, will not be resolved until the Supreme Court rules.
Now, I won't rehash here my recent SCOTUSblog essay, which provides links to a wealth of resources (op-eds, briefs, academic articles, etc.) on this controversy. Instead I'll summarize the legal arguments against the individual mandate — though other Obamacare provisions are also constitutionally problematic.
At base, the mandate exceeds Congress's power to regulate interstate commerce under existing doctrine. The outermost bounds of the Supreme Court's Commerce Clause jurisprudence — the "substantial effects" doctrine to which Professor Roosevelt alluded — stop Congress from conscripting an inactive person into commerce even if it purports to do so pursuant to a broader regulatory scheme.
The Constitution simply does not permit the government to compel citizens into transactions to remedy what would otherwise be an economic hole in a given piece of legislation. Although the Necessary and Proper Clause allows Congress to adopt reasonable means to regulate interstate commerce, it is not a blank check permitting Congress to ignore constitutional limits by manufacturing necessities. Indeed, any law — "necessary" or otherwise — that would transform Congress's authority into an open-ended power to legislate for "the general welfare" is unconstitutional.
While government lawyers emphasize the "uniqueness" of the health care market and the wisdom of the legislation at issue, "this case is not about whether the Act is wise or unwise ... in fact, it is not really about our health care system at all. It is principally about our federalist system, and ... the Constitutional role of the federal government." Florida v. U.S. Dept. of Health & Human Services (Judge Roger Vinson's decision striking down the individual mandate and with it all of Obamacare, Jan.31, 2011).
As the Congressional Budget Office put it nearly 20 years ago:
The government has never required people to buy any good or service as a condition of lawful residence in the United States. — CBO, The Budgetary Treatment of an Individual Mandate to Buy Health Insurance (1994).
Nor has Congress ever before imposed on every person a civil penalty for declining to buy a product. Even in the New Deal case of Wickard v. Filburn, the federal government claimed "merely" the power to regulate what farmers grew, not to mandate that people become farmers or buy farm products. (The government had previously defended Social Security's constitutionality in part by emphasizing that it didn't compel economic activity.) Even if not buying insurance is an "economic activity" — which would mean that every aspect of life is economic activity — there is no constitutional warrant for Congress to force people to buy a particular good or service.
Moreover — and touching on another issue Professor Roosevelt raised — while the substantial effects test is often conceived as purely a Commerce Clause doctrine, it actually interprets the Necessary and Proper Clause in the context of the power to regulate commerce. Consequently, the doctrine's limitations mark the boundaries of constitutional necessity and propriety. Because economic mandates do not fall within those limits, Congress cannot impose them under the guise of regulating commerce.
Even if economic mandates are deemed "necessary," however, they are not "proper" because they do not, as Chief Justice John Marshall put it in the foundational case of McCulloch v. Maryland, "consist with the letter and spirit of the constitution." Congress can require us to pay taxes, serve on juries, or register for the draft, but these very particular mandates relate to the duties of citizenship and the functioning of the republic, not the regulation of commerce.
In short, upholding the power to impose economic mandates would fundamentally alter the relationship of the federal government to the states and the people; nobody would ever again be able to claim plausibly that the Constitution limits federal power.
* I use the term "Obamacare" simply because people colloquially refer to it that way — probably because it's easier to say than "PPACA," "Affordable Care Act," or anything else. While thought by some to be pejorative, I've never understood how that is (unless said with a sneer, but by that standard anything can be pejorative). Even the leading academic supporters of Obamacare's constitutionality, such as Yale law professors Akhil Amar and Jack Balkin, use the term, as did Time's managing editor Richard Stengel in his recent cover story about the Constitution. The one accurate criticism I've heard is that the law was written by Congress, not the White House (for which the president got plenty of heat from the left). But that just means it would be better to call it Pelosi-Reid-care, which presumably is no more or less pejorative. In any event, that ship has sailed.