William Rehnquist's tenure on the Supreme Court presents a Sphinx-like riddle for students of the separation of powers: "What animal is that which in  the morning goes on four, at noon on two, and in the evening on three feet?" One might well answer: "Rehnquist's separation of powers jurisprudence, as it is a difficult creature to characterize, arguably evolving over time." In adolescence, it appeared an originalist on all fours, in manhood it walked erect, a Byron White functionalist, and in old age ... well, perhaps the Sphinx might just devour one after all! Indeed, it is difficult to identify a principle unifying the late Chief Justice's separation of powers cases.

And how does one explain the absence of any separation of powers revolution to accompany federalism's rebirth? No separation of powers opinion ever announced, "We start with first principles." Unlike federalism, well-favored and judicially policed by the Federalism Five, the separation of powers has arguably been neglected (salutarily, some might say). But that neglect, salutary or not, has been inconsistent. Rehnquist did police (or attempt to police) the horizontal "parchment barriers" of separation from time to time. What principle explains Rehnquist's philosophy of the separation of powers?...