Is Obamacare Constitutional?

Here (sorry, I think it is gated) is the latest angle from Steve Willis and Nakku Chung in the debate taking place in Tax Notes Today. Not being a legal scholar, I have trouble understanding how Obamacare differs from any other tax or subsidy in any substantively meaningful way. As such, I find it interesting how the legal scholars are drawing the distinction, and you will find discussion of these points at the above link. Unfortunately, this debate itself seems to just boil down to philosophical difference of opinion on the constitution. As Willis and Chung write in the beginning:

Congress has limited enumerated powers. We view the limitations seriously. We understand that much academic literature disagrees. Kleinbard recognizes few, if any, important limitations on congressional power -- either to tax or to regulate commerce. He joins the academic majority in supporting Congress's role in solving problems, including those it created. While he would limit congressional power to choose our television shows, he provides no reasoning for his limitations other than that they are his. Fundamentally, that is the issue. Do we follow the limitations on congressional power found in the Constitution or do we largely ignore them, opting for a living-document approach that bends (some might say breaks) over time? Neither viewpoint is provable. Both are honest approaches to American law; yet they differ fundamentally, which colors this debate.

Assuming Willis and Chung are correct, and since they are the legal scholars I will assume they are, then I have to wonder if any constitutional challenge of Obamacare will constitute a Supreme Court showdown of the "correct way" to interpret the constitution.