As we all wait on pins and needles, I thought I would engage in some completely idle, pre-decision spin and speculation. None of this speculation is remotely falsifiable; there is no way of testing its accuracy. Its just guessing, at best. Perhaps not even informed guessing. But what the heck.
Here is a thought I have had since the Court granted certiorari back in November. Might the Court (or at least the center of the Court) care more about a number of other issues heading the Court's way in the next few Terms--issues like affirmative action, campaign finance, voting rights, gay marriage, and the like? And might deciding this case in favor of the ACA's constitutionality essentially buy the Court a great deal more leeway with Democrats (and perhaps the public more generally), which would permit the Justices a much freer hand to pursue a more conservative agenda with respect to these other issues?
Much has been discussed recently about public opinion and its impact on the Court's decision making. In this case, the American public seems reasonably split on the ACA as a whole, and rather significantly against the minimum coverage provision. But there is also a fair amount of support for the ACA and the individual mandate. Suffice it to say that the Court has plenty of political room to decide this case however it chooses without fearing a truly threatening political reprisal. No political coalition could mount any sort of credible threat to the Court in response to its opinion, at least under present circumstances. (The Republicans might conceivably have such power following a landslide in November, but they would also then have the power simply to repeal the ACA, rendering any attack on the Court pointless and counterproductive.)
What the Court might rightly fear, though, is a growing perception that its decisions are partisan. Bush v. Gore and Citizens United are not too far in the rearview mirror. If the Court, over a series of years, decides these highly partisan questions (referenced above) along fairly predictable partisan lines--with the five Republican appointees voting one way and the four Democratic appointees the other--it might well threaten the Court's long-term "diffuse support." As much research has shown, the Court's popularity does not seem to take much of a hit when it renders a decision with which the public disagrees. What seems to matter is the public's perception that the Court is acting based on the Justices' sincere views of the law. This may be ideological, but it is legal (or constitutional) in nature.
This suggests that the converse (or is it obverse?) may be true as well. That is, even if the Court renders decisions that a majority of the public (or close to a majority) supports in terms of immediate result, the Court could still suffer a hit to its prestige if the perception grows that those decisions can be explained in purely partisan terms.
Just to be clear, this problem is not necessarily of the Court's making. It stems in part from the historical circumstance that the Court's five predictably conservative Justices were appointed by one party, and its four predictably liberal Justices were appointed by another. It also stems from the historical circumstance that the major parties seem to cleave on strict partisan lines on most all of these constitutional questions heading to the Court. Moreover, for this dynamic to create problems for Court, the public's perception need not be accurate. (Indeed, I personally think it would be quite wrong; to me, the Justices seem quite driven by ideology and deeply held constitutional views, but rarely, if ever, by partisan concerns.)
Thus, one could see the Court--or the center of the Court--deciding that the ACA decision is an opportunity for the Justices to make a show of their bipartisanship, a display of how it stands above the partisan politics infecting the other branches. Though certainly a lot of people would be very unhappy with the result, and would disagree sharply with the decision, such a decision could well (taking the longer view) enhance the Court's long-term prestige by being the salient counter-example to the Court's high-profile conservative decisions--including those likely to come, such as striking down Section 5 of the Voting Rights Act, upholding much (or all) of Arizona's S.B. 1070, and reaffirming Citizens United.
One more point to clarify. I am not suggesting that the Justices should act in this way. Nor am I suggesting that this would be a conscious aspect of their subjective thought processes. Rather, I am suggesting that, as a Supreme Court Justice--particularly a median Justice, or a Chief Justice--these sorts of circumstances are bound to seep into one's brain and subtly influence the way one sees the relevant precedents, legal arguments, and logical implications of the decision. The human brain works in all sorts of ways that we cannot perceive. Social psychologists attest that we often, imperceptibly, reach a result first, and then subjectively experience the analytic reasoning that leads to that result. The "real" reasons for the initial setting on a particular result never come into our subjective view.
In any event, if the Court upholds the individual mandate, these broader concerns may provide a plausible--albeit, completely unverifiable--explanation. Just a thought.