The great legal theorist Alexander Bickel advocated that courts use "passive virtues"—that is, using invented jurisdictional reasons to not hear politically contentious cases. The political scientist Mark Graber has tweaked this concept to describe passive-aggressive virtues—the tendency of the great Chief Justice John Marshall to expound on his theories of constitutional law while deciding cases on grounds that left opponents no means of opposing the Court (usually because they ended up with the policy they wanted.) In an intriguing article for Slate, David Franklin argues that the Roberts Court could duck the constitutional challenge to the Affordable Care Act using these methods. The Court, Franklin notes, could simply decide not to decide by holding that the legal challenge to the ACA is prohibited by the Tax Anti-Injunction Act. This would keep the court out of the political firestorm for the time bring while refusing to give Obama a political victory by clearly declaring the ACA constitutional.
Is this possible? Certainly. But I think Franklin's analogy overstates the political constraints facing the Roberts Court in this case, and therefore overstates the likelihood that the Roberts Court will deploy the passive-aggressive virtues. In this particular set of political circumstances, the Roberts Court can decide pretty much whatever it wants and make it stick without fear of serious political reprisal—which makes ducking the case less likely.
In Marbury v. Madison, for example, Marshall's maneuvering was a necessity borne of the fundamental weakness of the Court—Jefferson would have refused an order to give Marbury his commission and Marshall knew it. The Pledge of Allegiance case the Court ducked involved a case where upholding the First Amendment claim would have been both enormously unpopular with both legislators and the public and would have been very difficult to enforce (requiring the supervision of countless school districts where the court's decision would be held in contempt and could be enforced only with expensive litigation). The Affordable Care Act, while politically divisive, is nothing like these cases.
First of all, the courts are most likely to duck issues when they fear political reprisal or think that political actors will not enforce their decisions. This is not, however, such a case. While the ACA is the centerpiece of the Obama administration's agenda, the 2010 midterms have fundamentally changed the political context. The coalition that passed the ACA could not be reassembled today; indeed, one house of Congress would strongly support a decision striking down the ACA and a majority of the other house consists of legislators who opposed the ACA or are lukewarm about it. Obama would be strongly critical of an adverse decision but there's no reason to believe that he would refuse to abide by it. As for the public, the ACA has never been terribly popular and polls suggest that at least in the short term a ruling holding the ACA unconstitutional would be popular with the public, especially if it applied only to the mandate.
The legal scholar Mark Tushnet has argued that during periods of divided government the courts have a very broad range of discretion because they can count on substantial political support. The ACA is a case in point; however it ruled the Court would enjoy enough political support to make a decision stick and would not have to fear meaningful retaliation. This doesn't make it impossible that the Court will duck a ruling on the ACA, but it does make it less likely. Fundamentally, the Court's ruling on the ACA will depend on what the median vote in the Supreme Court wants to do, and this week's oral arguments will shed the first light on that. My guess is that the final outcome will involve a ruling on the merits.