A fair question. In a word, "Yes." At least that's my considered opinion.
The question is a bit misleading in some ways since, given that it is a putatively 'liberal' Justice who is retiring, and given also Obama's extraordinary caution not to provoke the loons on the Right, it is not possible that he'll EVER nominate anybody to the actual "left" of Ed Meese clone Anthony Kennedy.
So the answer is probably "yes, he will move the Court to the Right, since there is no way to move it to the Left without the death (!) or retirement of one or some of the OPUS Deists (Roberts, Alito, Scalia, Thomas, or Kennedy)...On TruthOut, prompted by speculation about the possibilities of Obama potential appointments in a NYTimes article, Jeff Cohen considers the alternatives and circumstances (originally on Common Dreams):
The centerpiece of the Times article was a fascinating study conducted by two University of Chicago law professors (one of whom is a conservative federal appeals judge) analyzing the judicial records of the 43 justices who've served on the Supreme Court since 1937. Four of the five most conservative judges of the last seven decades (Thomas, Scalia, Roberts, Alito) now sit on the Court. With Anthony Kennedy at number ten, five of the ten most rightwing judges are currently on the Court. The current majority, in other words, is almost a conservative all-star team.It's right in there: Except for Ginsberg, every nominee since 1971 has been more conservative than the person they were replacing.
By contrast, among the ten most liberal judges since 1937, the only sitting justice is Ruth Bader Ginsburg - she's number nine. Today's other three "liberal" justices (Stevens, Breyer, Souter) are in the top 15, but outside the top ten.
All in all, that's a rightwing-dominated Supreme Court.
The study gives credence to the claim of Justice John Paul Stevens (age 89) that he hasn't moved left since being appointed by President Ford in 1975, but that the Court has moved right. And it backs Stevens' assertion that "every judge who's been appointed to the Court" since 1971 "has been more conservative than his or her predecessor" - with the exception of Ginsburg (who recently underwent surgery related to pancreatic cancer).
The question facing Obama: Will he continue this trend of shifting the Court rightward?
Unfortunately, from what we've seen of Obama's general penchant for "moderate" appointees who don't inflame Republicans, it's quite possible the Court will continue trending rightward - if liberals get replaced with less liberal appointees. After Souter, the seats Obama is most likely to fill are those of the two most liberal justices: Ginsburg and Stevens.
So the real question is not whether or not an Obama appointee to the SCROTUS will move the Court rightward; it is, rather, how much and how far Rightward will it go?
We forget to our peril that, in fact, the Warren Court was an anomaly and an accident of history. So, even though the country appears marginally to move incrementally, glacially, to the left of center in so many ways--especially having to do with tolerance--the country's institutions continue to atrophy around "conservative CORPORATE principles," such "liberals" as Ginsberg notwithstanding. As a matter of interest, though, the last person actually rejected by the Senate was certifiable wingnut-libertrarian crackpot Robert Bork, so there's that...whatever "that" is.