OK, now we're having a big debate about the implications of the Roberts decision. Obviously, there are major implications: First, the ACA has been pulled back from the flames and there are all sorts of things that follow from that. Second, Republican governors of poor red states now get to screech and scratch and hop around like baboons in faux outrage at the temerity of the People of the United States in Congress assembled deigning to try to help people in their state get healthcare coverage. Maybe some of them will actually prevent it, and that's also the result of the Roberts decision.
But there is another, strictly political aspect of the decision that is riling the waters of the presidential election: the discussion of whether the ACA is a penalty or a tax.
There are several different viewpoints on penalty versus tax. The Obama administration (and maybe Romney himself) view it as a penalty and do not think it is a tax. The Rightwing reverberation chamber has now switched their attention completely from jobs, it seems, and now are intent on repealing the ACA because not only is it “government run healthcare” but it is the “largest tax increase in history”. In other words, they now claim it is a tax. Lots of other people think that it's sort of a tax and sort of a penalty. It's a “penalty tax”.
But none of these positions are based on the Robert's decision! (The “sort of, sort of” position is close.)
In fact, in his majority opinion, Roberts never actually says the penalty is a tax.
If you don't believe me, go read it yourself.
By my count, he said it could be: “reasonably read”, “construed”, “framed”, “treated”, “viewed”, “be characterized”, “interpreted”, and, ultimately, “sustained” as a tax. But, he never actually made the assertion everyone is claiming that he did. For Roberts, it remains a penalty that for constitutionality purposes can be be construed, etc., as a tax.
If you read beyond the Roberts opinion, you will find that the dissenters claimed that he did, but Roberts himself skated all around it without actually making that assertion.
In lawyerly fashion, Roberts' opinion goes to great lengths to find a way to construe, for the purpose of finding the law constitutional, that penalty as a tax, and he found what he needed in the wording of the ACA. But that doesn't mean that he considers it to be a tax.
Here's an illustrative example: in some variants of Poker, certain cards are considered wild, meaning they can be played as if they were any other card. Let's say you play a two as an ace. For the purposes of that hand, that two is construed as an ace for the purposes of giving you a pair of aces. But the two is not actually transformed into an ace, it remains a two for all other purposes.
Similarly, the penalty in the ACA remains a penalty; it simply was construed by Roberts as a tax for the sole purpose of finding constitutional that portion of the law.
So I believe that the best way to think about this part of the individual mandate is that it is fundamentally a penalty, but that it resembles a tax closely enough that Roberts was able to find the ACA constitutional under the taxation power of the federal government.
In other words, a wild penalty, played as a tax.