Well, other than being the first woman on the Supreme Court.

As one begins to consider whether O'Connor might be left with no similarly enduring achievements, it's worth pointing out that some part of this may well be of her own doing: Even at the height of her influence at the high court, O'Connor's critics tended to deride her constitutional stylings as closer to Muzak than Mozart. Justice Antonin Scalia once famously wrote that her argument in an abortion case "cannot be taken seriously." And her many critics often pointed to the lack of real rigor in her "undue burden" test for abortion restrictions; her "reasonable observer" test for whether the government has "endorsed" religion; or her "someday my prince will come" test for when affirmative action programs might become unnecessary in the future.

That's why Charles Krauthammer once wrote of O'Connor that "she had not so much a judicial philosophy as a social philosophy. Unlike a principled conservative such as Antonin Scalia, or a principled liberal such as Ruth Bader Ginsburg, O'Connor had no stable ideas about constitutional interpretation." Buried in this criticism was the implication that her legal framework would go easily, once she was replaced by someone with a "serious" constitutional theory. Samuel Alito, her successor, is probably that someone, at least from Krauthammer's point of view. Certainly no one would suggest calling him a "moderate," a "pragmatist," or a "common-law judge." Alito has an agenda far broader than O'Connor's one-case-at-a-time approach. It's hardly surprising that he has not taken up where she left off.

It isn't just her replacement by a more conservative justice. it is that there was never any coherence in her jurisprudence. Constantly trying to split the difference, her positions were often ad hoc compromises that were difficult to apply in real world settings. Indeed, her opinions really offered no more Constitutional clarity than Potter Stewart's "I know it when I see it" standard on obscenity. As such, the latter years of her time as a justice will likely be remembered as an interregnum during which there was little, if any, certainty on Constitutional matters, and even fewer principled decisions enunciated.