Did Justice Stevens change or did the Court change? My co-bloggers may be interested in debating this from a doctrinal perspective. But the data seem clear: Beginning in the mid-to-late 1980s, Justice Stevens moved substantially to the left.
The graph below uses measures (https://mqscores.wustl.edu/) developed by Andrew Martin and Kevin Quinn to plot the ideology of Justices Stevens, Kennedy, and Scalia: the higher the number, the more conservative the justice.
Note Justice Scalia's slight rightward drift and Justice Stevens' more extreme movement to the left. As for the Court's center, Justice Kennedy, not much in the way of drift in either direction. — Lee Epstein