A debate over Obamacare between me, Cal-Irvine law professor (and dean) Erwin Chemerinsky, and Demos’s Anthony Kammer is currently ongoing at PolicyMic.com. Below is my initial post, but the debate continues in the comments section. If anyone is so disposed, I invite you to join the conversation.

Congress has limited, enumerated powers under the Constitution. One of those is to regulate interstate commerce, which means ensuring that commerce flows easily between the states. Although the Supreme Court has expanded that regulatory authority to reach local economic activity that, in the aggregate, has a “substantial effect on interstate commerce,” Congress still lacks the power to compel citizens to enter into commerce for the purposes of regulating them—which is what the Affordable Care Act’s “individual mandate” does. Moreover, the penalty for not complying with the mandate is not a tax and, if it is, it is an unconstitutional one because it is not apportioned by population. That point is especially noteworthy because the individual mandate was passed in part to avoid the political accountability that raising taxes would have brought.

Those are my claims. But I’m going to concentrate my initial thoughts in the clouds, so to speak, rather than the weeds. I begin with a crucial point: enforcing limits on governmental power—especially Congress’s commerce power—is not and never has been about discovering limits to the power. Instead, it is about defining and enforcing those limits. Since the landmark commerce power cases of the late ’30s and early ’40s, however, the Supreme Court has largely treated the limits on federal power as detectable rather than definable. Those cases looked at our system of commerce as a pond and Congress’s power as extending over the ripples caused by disturbances on the surface. And if the effects of a single water bug or pebble were not detectable enough, we were told to imagine the combined effects of all those water bugs or pebbles.

That theory differs from how the Court looked at the commerce power before the New Deal, when Congress’s power was limited by type rather than degree. In other words, activities such as “manufacturing” were deemed off-limits to Congress not by virtue of the effects they had on interstate commerce—the ripples in the pond—but by virtue of the type of thing it was. Even though it produced items for commerce, manufacturing was local in nature, so Congress had no power to regulate it. Thus limits were articulated, rather than discovered.

Although many people thought that the Supreme Court abandoned this line of thinking during the New Deal, the Court reaffirmed that type-versus-degree distinction in the 1995 case of United States v. Lopez (followed in 2000 by another similar case). In Lopez, the Court struck down the Gun-Free School Zone Act not because guns in school zones don’t cause sufficient ripples in the national commercial pond, but because a gun law is fundamentally different from a commercial regulation. Indeed, the Framers knew that, if conceived broadly enough, everything has an effect on commerce. The ripples in the pond can affect the sand on the shore and even the animals on the land. Unless a distinction is drawn between the sand and the water—or, to leave that analogy, between buying something and not buying something—Congress’s power is unlimited.

With the individual mandate, we also distinguish power by kind rather than degree. Not only is the decision not to buy insurance not commerce, the idea that such a decision falls under Congress’s regulatory authority because it affects commerce is dangerous precisely because it is correct: of course decisions not to buy something affect commerce (indeed, any decision, action, or inaction ultimately affects commerce). Giving the government the power to regulate those decisions removes all limits on federal power.