The most important thing about the decision is that I had a dream last night in which the Supreme Court ruled 5-4 to uphold the constitutionality of the Affordable Care Act, with Roberts rather than Kennedy casting the decisive vote. I even put that on Twitter and Facebook at around 7:15 am, so there's a record of it.
And that's exactly what happened. Weird, huh? I have to look into ways to monetize my dreams.
Anyway, I'll leave it to others to analyze my psyche and the constitutional arguments, but I'll say a couple of quick things about the politics.
You'll hear a lot about who this helps or hurts. I would caution that for most Americans -- particularly the persuadable swing voters -- the news of Ann Curry leaving the Today Show is a much bigger deal at the moment, so let's not imagine that we're going to see any big shift in the polls.
Some will argue that the ruling will fire up the conservative base, who now absolutely need for Romney to win if they hope to undo ACA. I doubt it will make a big difference -- by November, the conservative base will presumably believe the re-election of Obama would usher in the United States of Black Panther Nation -- but it could give Romney a little bit of breathing room with his base through the convention. Perhaps he'll feel able to take a somewhat conciliatory stand on immigration, for instance, without worrying about conservative backlash.
You'll also hear that the ruling will give a political boost to Obama, by vindicating his signature achievement. I don't know about that. But I do think he might get a slight advantage with those persuadable voters. With the law upheld, and Romney pledging to repeal it, that puts a lot at stake for middle-of-the-road voters who have a specific (non-ideological, non-partisan) reason to care that it survives -- seniors in the "donut hole", 20-somethings on their parents' insurance; people with pre-existing conditions, and so forth. By contrast, those middle-of-the-road voters who oppose ACA don't have those kinds of personal motivations, and since middle-of-the-road swing voters are by definition pretty non-ideological and non-partisan, it's pretty hard to imagine many of them caring enough to have it affect their vote.
I would guess that in most cases, a similar dynamic will be at play in congressional races as well. So, possible slight advantage to Democrats in close races, I suspect.
Regardless, any effect is likely to be on the margins.