When conservative justices support criminal defendants (and liberal justices do not)

We generally assume that "conservative" judges are more likely to support the police and prosecutors, whereas "liberal" judges are more likely to support criminal defendants and safeguard the rights of the accused. No doubt these stereotypes are grounded in observed behavior. Yet there are cases and causes that confound this conventional account. Today's Supreme Court decision in Commonwealth of Puerto Rico v. Sanchez Valle is just such a case.

The Sanchez Valle case involves a criminal defendant's challenge to his prosecution for gun trafficking in Puerto Rico. According to the defendant, the prosecution was unconstitutional because he was also prosecuted for the same illegal gun transactions under federal law. For this reason, the defendant alleged, the prosecution violated the Fifth Amendment's prohibition on double jeopardy because Puerto Rico and the federal government, for these purposes, derive their sovereignty from a single source.

In a 6-2 decision, the Supreme Court agreed with the defendant, concluding that the Fifth Amendment's Double Jeopardy Clause "bars Puerto Rico and the United States from successively prosecuting a single person for the same conduct under equivalent criminal laws." The opinion for the court, written by Justice Elena Kagan, was joined by Justice Ruth Bader Ginsburg and all four of the court's conservatives. The two dissenting justices, who would have allowed the criminal defendant to be prosecuted more than once, were Justices Stephen Breyer and Sonia Sotomayor. So, in this case at least, the two most pro-prosecution justices were two of the court's more liberal members. Go figure.

UPDATE: It's also worth noting that Justice Ginsburg, joined by Justice Thomas, wrote a separate concurrence suggesting a need to rethink a central element of current Double Jeopardy doctrine. Her opinion reads:

I join in full the Court's opinion, which cogently applies long prevailing doctrine. I write only to flag a larger question that bears fresh examination in an appropriate case. The double jeopardy proscription is intended to shield individuals from the harassment of multiple prosecutions for the same misconduct. . . . Current "separate sovereigns" doctrine hardly serves that objective. States and Nation are "kindred systems," yet "parts of ONE WHOLE." The Federalist No. 82, p. 245 (J. Hopkins ed., 2d ed. 1802) (reprint 2008). Within that whole is it not "an affront to human dignity," Abbate v. United States, 359 U. S. 187, 203 (1959) (Black, J., dissenting), "inconsistent with the spirit of [our] Bill of Rights," Developments in the Law-
Criminal Conspiracy, 72 Harv. L. Rev. 920, 968 (1959), to try or punish a person twice for the same offense? Several jurists and commentators have suggested that the question should be answered with a resounding yes: Ordinarily, a final judgment in a criminal case, just as a final judgment in a civil case, should preclude renewal of the fray anyplace in the Nation. . . . The matter warrants attention in a future case
in which a defendant faces successive prosecutions by parts of the whole USA.