A bit of a speculative SCOTUS post to start the day...
I agree with Scott Lemieux, Matt Yglesias, and others that people make far too much of the idea that the primary job for a liberal Supreme Court nominee is to entice Justice Kennedy over to the liberal side.
Not just because the Supreme Court doesn't actually work that way, and because it miscasts Kennedy as a passive weakling. Mainly, because Elena Kagan is, if all goes well, going to be on the court for decades. Anthony Kennedy, on the other hand, isn't.
Which brings me to my point, which is that it's possible that thinking about persuasion in terms of individual cases is all wrong. The real thing for which Kagan -- and Obama -- need to persuade Kennedy to do is to consider retiring with a Democrat in the White House. For that, it really might pay to avoid a "a full-throated counterweight to the court’s conservative leader, Justice Antonin Scalia." Kennedy will turn 74 this summer. I've always said that it's a mug's game to make predictions about politicians and retirements, and that must be even more true about Justices on the Supreme Court. I would say, however, that if he considers retiring over the next several years, and if he cares about what happens to the Court after he's gone...well, if those things are true, then it's pretty easy to imagine the incentives involved and how Obama's nominees change those incentives. We can assume that Kennedy would prefer to be replaced by someone similar to himself, and then guess at where he perceives the next Democratic and the next Republican appointments would be. Presumably, given his voting pattern, he'd prefer to be replaced by a Republican appointee -- but relatively moderate picks by Democrats might close that gap somewhat (as might extremist rhetoric from Republican candidates). If he does reach a point at which he'd prefer retirement, but Obama or another Democrat is president, it may be that if he perceives a relatively smaller gap between himself and a likely Democratic nominee that it might make a difference between him pulling the trigger or waiting another four (or more) years. Perhaps if it's going to be Brennan or Marshall, he stays; if it's going to be Breyer, well, that makes it a bit easier to walk. Especially if Sarah Palin, Rush Limbaugh, and Glenn Beck are the arbiters of Constitutional Law within the Republican Party.
Is that worth choosing a moderate liberal over a "full-throated" liberal? I have no idea; but then again, I don't really think there's any good way to know which one Kagan is going to turn out to be, assuming she is confirmed. As I said, just a bit of speculation to add to the mix.