Justice Clarence Thomas, joined by Justice Scalia, wrote an interesting concurrence in yesterday's partial birth abortion case, indicating that he might be sympathetic to a Commerce Clause challenge to the federal partial birth abortion ban that was just upheld by the Court. At the oral argument, liberal justices Ruth Bader Ginsburg and John Paul Stevens also suggested that they believe that at least some applications of the statute exceed Congress' enumerated powers under the Commerce Clause. I discuss their concerns in more detail here and here.

Assuming for the sake of argument that these four justices would all support a Commerce Clause challenge to the statute, could they pick up a fifth vote? It is difficult to know for sure, but the answer may well be yes. As I explained at the time of his nomination, Justice Alito had a strong record of support for limits on federal power as a court of appeals judge, and he might well continue in that vein on the Supreme Court. It is also possible, though far less likely, that Justice Souter or Justice Breyer (who wrote the Supreme Court's earlier partial birth abortion decision, Stenberg v. Carhart), would place their commitment to abortion rights ahead of their commitment to virtually unlimited federal power.

All of this is of course highly conjectural. Predicting justices' votes on the basis of remarks in oral arguments is a chancy business. Ditto with predictions based on opaque concurring opinions. Only in the case of Justice Thomas am I close to certain about what his vote will be. The other four are considerably more difficult to predict. Moreover, whether or not a Commerce Clause challenge to the partial birth abortion ban succeeds will depend in part on the specific facts of the case. A case addressing a partial birth abortion in a nonprofit clinic involving a woman who did not cross state lines, would be more likely to succeed than one with a commercial clinic or an interstate transaction.

Nonetheless, there is at least some significant chance that a cross-ideological coalition of justices would be willing to support a federalism-based challenge to the congressional partial birth abortion ban. If it does come to pass, it will be hugely important as the first Commerce Clause case in decades where federal power was constrained by a coalition of liberal and conservative justices rather than by a narrow 5-4 majority consisting of the five most conservative members of the Court. In my view (see here for details), judicial enforcement of limits on federal power cannot survive in the long run if it remains a parochial concern of conservatives and libertarians. Just as with judicial enforcement of free speech, freedom of religion, and other constitutional constraints on government power, it requires a broader cross-ideological consensus in order to succeed.