Randy Barnett has been following litigation in response to the individual mandate of the healthcare legislation that the Democrats rammed through Congress. Noting that the Obama administration’s reliance on a claim of Congress’s taxation power proves that arguments against the legislation’s claims of Commerce Clause authority were never “frivolous,” Barnett explains that the law, itself, relies on the now-challenged self justification. In other words, for the Supreme Court to uphold the mandate, it would have to “look behind that characterization during litigation to ask if it could have been justified as a tax.”
Even so, Barnett doesn’t think the tax power argument will fly with the current Supreme Court (emphasis added):

Now, of course, the Supreme Court can always adopt these two additional doctrines. It could decide that any measure passed and justified expressly as a regulation of commerce is constitutional if it could have been enacted as a tax. But if it upholds this act, it would also have to say that Congress can assert any power it wills over individuals so long as it delegates enforcement of the penalty to the IRS. Put another way since every “fine” collects money, the Tax Power gives Congress unlimited power to fine any activity or, as here, inactivity it wishes! (Do you doubt this will be a major line of questioning in oral argument?)
But it gets still worse. For calling this a tax does not change the nature of the “requirement” or mandate that is enforced by the “penalty.” ALL previous cases of taxes upheld (when they may have exceeded the commerce power) involved “taxes” on conduct or activity. None involved taxes on the refusal to engage in conduct. In short, none of these tax cases involved using the Tax Power to impose a mandate.

Of course, some not-insignificant portion of ObamaCare supporters ultimately believe that Congress does have unlimited power over individuals. It’s encouraging to know, therefore, that there are folks with the interest and resources to fight on our behalf.