So who will Obama nominate to replace David Souter? Ideologically, probably someone who's not all that different. But it's worth remembering that Souter's real legacy is that he's the one who made Supreme Court appointments the artery-hardened slugfests they are today. It's not his fault or anything, but he was supposed to be a conservative strict constructionist when George H.W. Bush appointed him, and then, over time, turned out not to be. In 1992 he voted with the pro-choice contingent in Planned Parenthood v. Casey and after that became a steadily more liberal influence on the court. The conservative rallying cry following this slow-motion defection became "No more Souters!" and liberals learned the Souter lesson too. The result: nobody gets nominated anymore unless their judicial temperament is fully and unequivocally cast in stone. The market for moderates and interesting thinkers is pretty much gone.
And all because of mild mannered David Souter. Who would have guessed?