Posner begins by puncturing the myth that judging can ever be completely apolitical. In constitutional cases, he shows, the Court is unavoidably "a political body ... exercising discretion comparable in breadth to that of a legislature." The most sincere attempt at "lining up the facts alongside the constitutional text" usually provides no more objective a basis for preferring one outcome to another than for "preferring a margarita to a cosmopolitan."
Next Posner explains that the justices would look and act less like political manipulators if they "acknowledged to themselves the essentially personal, subjective, and indeed arbitrary character of most of their constitutional decisions." Such self-awareness is rare among justices, Posner says, because it "would open a psychologically disturbing gap between their official and their actual job descriptions."
Instead, "cocooned in their marble palace, attended by sycophantic staff, and treated with extreme deference wherever they go, Supreme Court justices are at risk of acquiring exaggerated opinions of their ability and character."
The path of wisdom would be to acknowledge that "the law made me do it" is usually no more than a "rationalization for the assertion of power" of an essentially political nature, Posner adds. Justices who understood this would probably be "less aggressive upsetters of political and policy applecarts than they are."
These are all drawn from a November 2005, Harvard Law Review article entitled "Forward: A Political Court"
Posner argues that if the Supreme Court is inevitably a political court, because it is a constitutional court, that it should seek to be "modest" rather than "aggressive" in its rulings. I don't agree that this is a good guideline.
There are times when a light touch is appropriate, and times when the Supreme Court needs to take a bold role. In my view, the Supreme Court's justices need to have a philosophy of government that underlies its public law rulings, which is rooted in our constitutional tradition. This philosophy removes the ambiguity that the text itself leaves us, by providing context for those provisions being present, which in turn makes interpreting them easier. This is not a true "umpire role" in the sense that the rulings do not derive from narrow rules, but it is also not an unbounded role. The problem with the court is not that its decisions are whimsical, but that the political bodies that have appointed it have left it divided on what philosophy of government should inform the document that is the basis of our political community.
I'll also mention some statistics in the underlying article because, well, I was a math major and I am a policy wonk and I just like statistics.
The courts immediately below the U.S. Supreme Court are the U.S. Courts of Appeal and the state supreme courts. In the most recent data available when he wrote the article, the former decided 56,396 cases (up from 3,753 in 1959, about half of which in each case were decided on the merits) and the later about 25,000 cases. Another 130,000 cases were decided by intermediate state appellate courts and thus were revieweable by the U.S. Supreme Court if certiorari was denied by a state supreme court. From the federal cases, just 64 were granted review in 2004, and from the state cases, just 23 were reviewed. Thus, inevitably, policy making on ambiguous issues must prevail over error correction.
Posner also notes that while the percentage of cases handled by the Supeme Court relating to constitutional issues varies (since 1955 from about 25% to 65%), that in recent years it has hovered between 30% and 50% of the caseload, and that 80% of constitutional cases in a recent year were split decisions, while only 63% of statutory cases were split decisions.
Finally, while not strictly statistical, pages 74-74 of the article, using the law review numbering, where Posner notes from Rehnquist's comments that very few minds are changed in the conference of the judges on a case and that the Supreme Court, is, in practice, not very influenced by deliberation as opposed to votes, is also a worthwhile observation.