Here is the opening of my article:
Why do some Republican Supreme Court Justices “evolve” over time, becoming more liberal than they were—or at least more liberal than they were thought likely to be—when they were appointed, while others prove to be every bit as conservative as expected? For nearly four decades, one single factor has proven an especially reliable predictor of whether a Republican nominee will be a steadfast conservative or evolve into a moderate or liberal: experience in the executive branch of the federal government. Those who lack such experience evolve; those who have had it do not.The bulk of the article goes about proving these points and offering a causal explanation: I hypothesize that Republican Presidents and their legal advisers have been using prior federal executive branch experience to sort true believers from moderates. Because of the long lead time for law review publications, when the article went to press, I did not yet have data for the full 2006-07 Term, but this last Term now dramatically confirms the pattern: as predicted, Roberts and Alito proved to be very reliable conservatives.
. . . Since President Nixon took office in 1969, the Senate has confirmed twelve Supreme Court nominees of Republican Presidents. Of these, six have had no substantial federal executive branch experience: Blackmun, Powell, Stevens, O’Connor, Kennedy, and Souter. The six successful Republican nominees who have had substantial executive branch experience are Burger, Rehnquist, Scalia, Thomas, Roberts, and Alito. Although it is too soon to make firm judgments about the two most recent appointees, it is notable that every one of the Justices on the first list has been less conservative than every one on the second list. And preliminary evidence indicates that the pattern will also hold for Chief Justice Roberts and Justice Alito.
However, the most recent Term casts some doubt on my claim that during the period under study, every Justice with prior federal executive experience has been more conservative than every Justice without such experience. In particular, the recently completed Term casts doubt on the claim that Chief Justice Burger was more conservative than Justice Kennedy. After all, it was Chief Justice Burger's majority opinion in Swann v. Charlotte-Mecklenburg Bd. of Educ. that said: "School authorities . . . might well conclude . . . that, in order to prepare students to live in a pluralistic society, each school should have a prescribed ratio of Negro to white students reflecting the proportion for the district as a whole. To do this as an educational policy is within the broad discretionary powers of school authorities." Justice Kennedy joined in part the opinion of Chief Justice Roberts striking down the efforts of Seattle and Louisville to do just that in the Parents Involved case. Moreover, Justice Kennedy voted with the conservatives in 13 of the 19 cases that split 5-4 along ideological lines (see chart on Scotusblog here). Thus, while Justice Kennedy is pretty clearly less conservative than Roberts, Scalia, Thomas, and Alito (as well as Rehnquist), it is not perfectly clear that he is less conservative than Burger was.
Like Kennedy, Burger voted for a right to abortion (in Roe), but later indicated that he thought the right narrower than his more liberal colleagues did (as indicated here). And as the dicta from Swann indicate, on race issues, Burger was arguably less conservative than Kennedy. In the other direction, Kennedy has been the Court's leader on gay rights, sweeping away Bowers v. Hardwick, including CJ Burger's (offensive) concurrence in that case. And Kennedy is a free speech liberal while Burger was not.
It's not entirely clear how one meaningfully measures whether, in the aggregate, Kennedy is more or less conservative than Burger was, but that's largely beside the point. At most this exercise shows that Burger is a possible counter-example to my thesis, but I do not claim in the Article to have discovered a law of nature, just a strong correlation in an admittedly small data set. And even then, I'm not willing to concede that Burger is a counter-example. Ideology, I think, needs to be measured in relative terms. On a Court that included William O. Douglas, William Brennan, and Thurgood Marshall---and on which Harry Blackmun and John Paul Stevens counted as moderates---Burger was very clearly conservative. Likewise, on the Rehnquist and Roberts Court, Kennedy is clearly a moderate/swing Justice.