Weigel, at his WaPo digs, explains why Bill Kristol called Elena Kagan a "a very respectable choice":
...Justice Antonin Scalia has beamed about how smart she is. Fairly or unfairly, conservatives don't think that Justice Sonia Sotomayor has the pull with her colleagues to break the 5-4 conservative majority on important cases. They do think that Kagan could do this. There's a second reason you'll hear conservatives praise Kagan, and Glenn Greenwald captured it well -- many believe she is more deferential to executive power than Justice John Paul Stevens turned out to be. So I think there's a combination of respect and bargaining at work here.