Ideological Drift Among Supreme Court Justices: Who, When, and How Important?

I. INTRODUCTION When the U.S. Supreme Court invalidated the use of military commissions for enemy combatants in Hamdan v. Rumsfeld? the decision fueled more than a national debate over the powers of the President. It also generated commentary about the ideological composition of the Court. Conservatives proclaimed that they were just one Justice, just one vacancy, away from victory in Hamdan2 and a handful of other recent decisions that worked against their interests.3 Liberals worried about it just as much.4 The commentary over Hamdan reflects a widely shared belief among journalists, politicians, scholars, and even judges: alterations in the Court's jurisprudence are unlikely in the absence of membership change. That is because of an underlying belief that the Justices themselves do not exhibit ideological change over the course of their tenures.5 To paraphrase the old proverb: once a conservative, always a conservative. Likewise for liberals.6 Why the assumption of stable preferences is so deeply held is open to speculation. Some analysts suggest it would defy logic to expect mature persons, with years of experience in the legal world, to revisit their jurisprudential views. Would a John G. Roberts Jr.-a Justice who has studied, litigated, or adjudicated court cases for over half his life-alter his ideological preferences? The answer, according to Professor David A. Strauss, is that he would not: As Americans try to figure out what Judge John G. Roberts Jr. will be like as a U.S. Supreme Court [JJustice, one idea seems to [be] that whatever Judge Roberts is now, once he is on the [CJourt he might develop into something different. In particular, the thinking goes, even if he is the intense conservative suggested by his Reagan-era memoranda, he may become more moderate as a [J]ustice. Don't believe it.7 Shoring up intuitions about the implausibility of preference change is empirical support in the form of a William H. Rehnquist on the right and a Thurgood Marshall on the left-Justices who never seemed to veer from their preferred ideological courses. When President Richard Nixon appointed Rehnquist to the Court, virtually all observers of the day deemed the nominee a reliable conservative.8 Likewise, at the time of his appointment, the press declared Justice Marshall a probable addition to the Court's "liberal bloc."9 That these initial ideological labels well characterized the Justices' future behavior only serves to confirm Professor Strauss's claim about the unlikelihood of change. Or so the argument goes. And yet, despite the commonplace nature of the claim, it is not without its share of skeptics. Whether pointing to anecdotes or more systematic evidence, several analysts now contend that ideological drift is not just possible but likely.10 Exhibit A, they say, is Justice Harry A. Blackmun. While the Justice himself maintained that it was the Court, not he, that moved-"I don't believe I'm any more liberal, as such, now than I was before," Justice Blackmun once told a reporter"-many scholars disagree.12 To them, it is hard to believe that the same Justice who dissented from the Court's 1972 decision to strike down existing death penalty statutes13 wrote, in 1994, "[f]rom this day forward, I no longer shall tinker with the machinery of death."14 But is Justice Blackmun the rule or the rare exception? Do most Justices remain committed to a particular doctrinal course throughout their careers, as Strauss and others contend, or do the skeptics have the better case? After reviewing the relevant commentary in Part II, we deploy state-of-theart methods to address these questions. The results, as it turns out, could not be clearer: contrary to the received wisdom, virtually every Justice serving since the 1930s has moved to the left or right or, in some cases, has switched directions several times. Finding that ideological drift is pervasive, in Part IV we develop the implications of our results for two moments in the Justices' career cycle: the events surrounding their appointments to the Court and the doctrine they develop once confirmed. …