Ben Smith quotes an anonymous conservative lawyer on the case for overturning Obamacare:

You have built an imaginary mansion, with thousands of rooms, on the foundation of Wickard v. Filburn — the 1942 ruling that broadened the understanding of how the Commerce Clause could be used to regulate economic activity.

We aren’t being asked to radically revise the Commerce Clause and throw out seven decades of law, and we won’t. But we know the founders never intended the Commerce Clause to allow the Federal Government to regulate everything on the planet. So we are going to accept Randy Barnett’s basically spurious exception to that basically spurious idea, and throw out the Affordable Care Act on the grounds that the Commerce Clause regulates “activity” (which we don’t really believe), but not “inactivity,” (because, why not draw the line somewhere?).

Wickard v. Filburn is the case in which the federal government fined Roscoe Filburn for growing wheat in excess of the quotas set out in the Agricultural Adjustment Act of 1938. They also forced him to destroy the excess wheat, even though he said it was only for personal use. The Supreme Court backed the government. Key quote:

Even if appellee’s activity be local and though it may not be regarded as commerce, it may still, whatever its nature, be reached by Congress if it exerts a substantial economic effect on interstate commerce and this irrespective of whether such effect is what might at some earlier time have been defined as ‘direct’ or ‘indirect.’

This is, I think, the most honest way to present the argument. Based on existing precedent, the individual mandate is clearly constitutional. Free riders in the health insurance market clearly have “a substantial economic effect on interstate commerce.”

But many conservatives believe the Supreme Court has been wrong on the Commerce Clause for seven decades now. The problem, in other words, isn’t so much the individual mandate as the large body of case law that makes the mandate — and so much else that the federal government does—constitutional. That’s where you get Republican politicians like Rick Perry arguing that almost everything the federal government does— Medicaid, Medicare, Social Security, etc —is properly understood as unconstitutional.

Conservatives know the Supreme Court doesn’t want to call the bulk of the federal government’s activities into question. But they also know that many of the Republican-appointed justices on the Court are uncomfortable with the post-Wickard Commerce Clause.

That’s where Barnett’s activity/inactivity distinction comes into play: It arguably gives the Supreme Court a way to reject the mandate without upsetting too much existing precedent, even as it leaves the Court in the odd place of saying it’s constitutional to tax you and use the proceeds to fund a single-payer health-care system but not constitutional to tell you to purchase health-care insurance so long as you can afford it.