The justices will hear two hours of arguments on the mandate today, after yesterday's rather technical arguments that dealt with the question of an obscure law called the Anti-Injunction Act.

But what might be surprising is that even some liberal justices might reject the government's argument that the mandate penalties for not having insurance are taxes and therefore, not subject to Supreme Court review.

Ilya Somin:

Justice Stephen Breyer suggested that the mandate is not a tax because "Congress has nowhere used the word "'tax.'" Justice Ginsburg noted that the mandate may not be a tax because it isn't a "revenue-raising measure," and because the monetary penalty is separable from the mandate itself. Justice Sotomayor also expressed doubts about whether the mandate is a tax, as did several for the conservative justices. As far as I can tell, none of the justices seemed to support the argument that the mandate is a tax.

Thus, today's events do not bode well for the federal government's constitutional tax argument. However, there are two caveats to this conjecture. First, the justices sometimes ask questions for rhetorical effect or play devil's advocate. I don't think they are doing so here, but obviously I can't be sure. Second, it is theoretically possible that the constitutional definition of what qualifies as a "tax" is broader than the AIA definition. This is not the usual view of the matter. Indeed, the one lower court that ruled that the AIA applies to this case did so precisely because they thought that the AIA's definition of "tax" is broader than the Constitution's. However, it's not completely impossible that the Court will reach the exact opposite conclusion, and the Solicitor General actually argued for such an approach today. However, there is no indication that the justices are leaning in that direction, or that any of them believe that the constitutional definition of a tax is broader than the AIA definition.

As Somin points out, however, opponents of Obamacare are a long way from victory:

Even if the federal government loses on the tax argument, they could still win on the Commerce Clause or the Necessary and Proper Clause. The latter is probably their strongest point.

We will probably get a better feel today for where some of the possible swing votes - Stevens and perhaps Breyer - come down on some of these issues.