The conventional wisdom holds that replacing Justice David Souter with Sonia Sotomayor will not have a significant effect on the Supreme Court's jurisprudence. For most high-profile, hot-button issues, this may be correct. Yet for reasons I have noted before (see here and here), I think that Sotomayor's confirmation could have significant effects, particularly in the area of criminal law. Last week's decision in Melendez-Diaz v. Massachusetts provides a nice illustration of how the Court's approach to some criminal law issues might change once Justice Sotomayor replaces Justice Souter on the Court.
In Melendez-Diaz the Court split 5-4 over whether the Confrontation Clause requires treating crime lab reports as testimonial evidence. The justices did not split along traditional ideological lines, however. Rather the division could be described as one between formalists and pragmatists. The former group -- Justices Scalia, Thomas, Stevens, Ginsburg and Souter -- sought to apply the Confrontation Clause in a formalistic manner, concluding that affidavits completed by forensic analysts are testimonial evidence that may only be admitted if the authoring analysts testify (or are unavailable), so as to allow a criminal defendant the opportunity to confront them. The latter group -- Justices Kennedy, Alito, Breyer, and the Chief Justice -- take a more pragmatic approach, concluding that the Confrontation Clause's requirements need not be applied so rigidly to scientific evidence. This is a split we've seen before, both in other Confrontation Clause cases, as well as in cases challenging the constitutionality of sentencing schemes that allow or require judges to make sentencing decisions based upon facts not found by a jury, so it is not isolated to this one issue.
Which camp will Justice Sotomayor join assuming she is confirmed to the Court? It is impossible to know for sure, but there are reasons to suspect that she may join the pragmatists more often than the formalists. For one thing, her criminal law opinions provide little evidence of a strong civil libertarian streak of the sort that would lead her to apply constitutional protections for criminal defendants in a strict and unyielding manner. Further, her experience as a trial court judge and prosecutor may lead her to take a more pragmatic, and less bright-line-oriented approach to these sorts of cases. If so, her ascension to the Court could have dramatic consequences for criminal law, as she could create a new Court majority on these issues and roll back recent decisions on the Confrontation Clause, sentencing rules, and other areas of criminal law.
Would such a change be a bad thing? That depends on how one approaches these sorts of cases. For myself, I am quite sympathetic to the formalist approach, and find Justice Scalia's arguments quite compelling (and not just because he cites one of my colleagues). So I think it would be unfortunate were she to depart from Justice Souter's approach to these questions. Reasonable people may differ.
Interestingly enough, the cross-ideological nature of the Court's split also ensures that this sort of case will receive less attention than others in the confirmation process. Cases with clear ideological divisions are ready-made for ideological activists and partisan Senators, and they are the easiest to squeeze into a conventional media narrative about the battle between Right and Left. Yet in this sort of case, there is no clear "conservative" or "liberal" position, despite the Court's narrow division. So, while this case illustrates more of what's "at stake" in the confirmation, it does not raise the sort of issue that is likely to receive significant attention in the debate over Sotomayor's confirmation.