First off, well done, Armando! Parts might be a little dense for DK's more general audience, but this case presents dense, not simple, questions. I disagree with some of Armando's judgments, but cordially and with considerable respect.
Below are responses to some of the points he makes not on the merits - that'll come during argument and as the Armando/Adam pieces unfold - but on the surround. As judges have been heard to say, "Let it in for what it's worth."
Why then is this case before the Supreme Court?
No, it’s not because SCOTUS is “just another political actor.” This case is there because litigants brought it there, in somewhat surprising agreement that the case is ripe and should be decided now and in advance of its full efficacy. And the court is there not because it is a political actor (Yes, the law is a political instrument and the Court can play on that fiddle when it chooses) but because Chief Justice John Marshall and a unanimous court settled the question in 1803 in Marbury v Madison – the Court has the power decide the constitutionality of laws enacted by Congress. With that awesome ability, the Supreme Court does not belong in the category of "just another."
[I]n the end, the Supreme Court does what it wants to do.
Well, Yes, Maybe, sort of by definition, I guess ... although some of us think the burden on the Court is heavier than that implies, for it does have precedent to deal with. As Armando points out, we should be happy it has precedents for I, like he, feel past decisions well support the constitutionality of ACA. If the Court does not agree, it probably will either create a relatively narrow line of law (which it is perfectly capable of doing!) or deny the idea of expansive Congressional power with a blunderbuss opinion (which, unless the court is venal and incredibly short-sighted, it is unlikely to do, much as J. Roberts might desire that). A bad result in my view would be one of those godawful cases where there is a bare majority decision but the rationales for it are so scattered and fractious that there is no majority opinion.
Is it fair or right to label Chief Justice Roberts or his predecessor Rehnquist “unprincipled.”
No. (Yeah, I know this is DK and I'm a Progressive, too, mostly ... but No.) As for J. Scalia, he is, as my boss used to say in a different context, “a man of principles, whose First Principle is flexibility.”
Justice Kennedy holds the answer.
Probably. Most commentators seem to think so and the litigants seem to be carving their arguments to appeal to him especially. But there are other members of the Court who must not be taken for granted. They, too, are influential legal scholars and compelling advocates. And then there are also oral arguments. One can only hope that those who so dislike ACA will do what Republicans have become so adept at doing, and over-state, over-react and harangue. (I thought of how this could backfire in writing about “unprincipled,” above.)
Escape hatch: election issue – Want to punt? Does the Court want to be an election issue?"
Interesting that the court scheduled three days of argument, unprecedented in modern times, only one of which focuses directly on timeliness. I think this Court is ready to decide but again, this is one of those cases where the oral arguments will have considerable influence. I doubt this one - which revisits one or more of the biggest ticket issues in governmental powers - has been conferenced in advance.