The prevailing wisdom is that replacing Justice David Souter will not have a significant impact on the Supreme Court's balance. For most high-profile, ideologically charged issues, this is probably true (at least in the near term). Justice Souter is generally quite "liberal," and anyone President Obama nominates is likely to be quite liberal as well. That said, I think there are two ways in which Souter's replacement could have a significant effect on the Court's balance and doctrinal trajectory.

First, Justice Souter's replacement could alter the balance of the Court on a number of issues on which the Court is closely divided, but does not split along the traditional left-right fault line. Consider, for example, this term's decision in Arizona v. Gant. Justice Stevens' majority limiting the search-incident-to-arrest exception to the warrant requirement was joined by Justices Ginsburg, Souter, Scalia and Thomas. Justice Breyer was in dissent. Other criminal law cases, including the sentencing guideline cases, have produced similar lineups. So, if Justice Souter's replacement were to align with Justice Breyer, instead of Justices Stevens and Ginsburg, we could have a significant shift on the Court. Indeed, replacing Justice Souter with a justice who follows Justice Breyer's approach to criminal law issues could actually move the Court to the "right" (at least on these issues).

Replacing Justice Souter could also have a significant effect is on the Court's decisions on the due process limitations on punitive damages. Justice Souter joined the five justice majorities in BMW v. Gore and Philip Morris v. Williams limiting the award of punitives on due process grounds, and also wrote the Court's majority in Exxon Shipping v. Baker, which limited punitive damages under the federal common law of maritime. Again, "liberal" justices are split on this question. Here, however, if Souter's replacement were to align with Justices Stevens and Ginsburg, it is likely that the Court's recent punitive damages cases could be overturned.

A second way that Justice Souter's replacement could alter the balance on the Court would occur behind the scenes. Adding a new justice inevitably alters the internal dynamic on the Court, and some justices are better coalition builders than others. Insofar as Justice Souter's replacement is more (or less) able to forge consensus and draft opinions that command wide support, this could also have a significant effect on the Court. Even were President Obama to replace Justice Souter with someone who votes identically on every issue, the nomination could still have a significant impact (especially over time) if the new justice is more able to influence his or her colleagues.

Many on the Left say they want President Obama to nominate a "liberal Scalia". I would say they should be careful what they wish for. Justice Scalia's opinions may be well-written and intellectually satisfying, but the same things that can make his opinions fun to read may prevent his opinions in many areas from commanding a majority of the Court. To take one example, documented by Professor Richard Lazarus shows in this paper, Justice Scalia's insistence on stronger bright-line rules for regulatory takings prevented him from creating a workable majority and produced "precedent heavy on strong rhetoric yet light on staying power." It's not an accident there's a book of his opinions called Scalia Dissents. So, perhaps paradoxically, a liberal nominee who demonstrates less ideological fervor, but is more strategic and conciliatory, might be more successful at moving the Court leftward.