Here's a link to a scholarly treatment from Berkeley that agrees Justices tend to shift over time (
link).
After reviewing the relevant commentary in Part II, we deploy stateof-the-artmethods 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 theleft or right or, in some cases, has switched directions several times.
Expectations are often satisfied:
These are the very patterns we observe in Figure 1.41 Indeed, with only scattered exceptions(e.g., the unexpected liberal voting of Harry Blackmun), press characterizations prior to appointmentturn out to be remarkably good predictors of future voting. To take one example, RuthBader Ginsburg reaches liberal decisions in about 60 percent of the Court’s cases—almost exactlythe percentage we would expect from a justice with her moderately left-of-center political outlook.Likewise, Antonin Scalia, assessed by all newspaper editors as a conservative at the time of hisnomination, votes precisely as that label would suggest, reaching right-of-center results in almostseven out of every ten cases he decides
But the authors understand the arguments of those who argue that you must observe votes along terms to see the shift they purport. After addressing the problems with that approach:
Using data derived from thevotes cast by the justices and a Bayesian modeling strategy, they have generated term-by-termideal point estimates for all the justices appointed since the 1937 term—estimates that attend tovariation in case content. In other words, using the Martin-Quinn approach we can offer intrajusticecomparisons (e.g., is Justice Souter more liberal now than he was in 1992?) without havingto consider whether the changes we observe are the result of differences in the content of cases orchanges in the justice’s revealed preferences.86
While a number of justices did indeed begin to list to the left over time, your author is incorrect in citing that as the trend. While Warren, Souter, Rehnquist, O'Conner and yes, Kennedy, trended left--
For now, consider those justices who, incontrast to Rehnquist and the others, trended to the right. Falling into this category, as we can seein Figure 7, are Justices Hugo Black, Harold Burton, Felix Frankfurter, Robert Jackson, StanleyReed, Antonin Scalia, and Byron White.
Eleven of the twenty six justices became more liberal over their tenure. Several shifted right. And a number went left and right over their tenure. Only four remained fairly constant.
So what we can say is that justices are more likely to move left, but that a significant percentage will move right and many will move a bit in either direction over time, with the least statistically significant group remaining constant (around 15%).
