Eric Posner's Slate SCOTUS Review: Are the Court’s Conservatives Dividing? (#UChiLawSCt)
One of the striking things about this term is that the Republican appointees are forming a significantly looser coalition than the appointees of Democratic presidents. If you look at these SCOTUSblog statistics showing when the judges at least partially agree in the opinion or judgment in the cases that are not decided unanimously (about half of the total), you will see that Sotomayor and Kagan agree 91 percent of the time, Sotomayor and Ginsburg agree 86 percent of the time, and Ginsburg and Kagan agree 86 percent of the time. Breyer does not march quite so much in lockstep, agreeing with each of the other three liberals between 67 and 76 percent of the time. (The statistics cover this term through June 12)
Now look at the conservatives. Everyone knows that Kennedy is a swing voter, and indeed he agrees with everyone else between 41 and 59 percent of the time. But I didn’t know that Kennedy actually agrees with the liberals more than with the conservatives (for example, 41 percent with Thomas, and 59 percent with Ginsburg). Who knew that so far this term, Scalia and Alito agree only 50 percent of the time? (This is historically unprecedented, and possibly a statistical anomaly, since they usually vote together.) The other conservative pairings range from about 64 percent to 77 percent. By way of comparison, conservatives like Roberts and Alito, and liberals like Sotomayor and Kagan, agree across ideological lines in the 18 to 41 percent range.
From glancing through the non-unanimous criminal procedure cases, my sense is that these patterns are even clearer. Sotomayor, Ginsburg, and Kagan virtually always vote in the same way—in favor of the criminal defendant. Breyer favors criminal defendants but votes in the government’s favor fairly often. Alito, Roberts, and Thomas almost always favor the government, Alito most of all. But the three of them do disagree with each other from time to time. Scalia favors the government but less than the other staunch conservatives. Kennedy, true to his reputation, favors the government half the time.