First are the ideology scores put out by Andrew D. Martin and Kevin M. Quinn of Washington University in St. Louis. The so-called Quinn-Martin scores show the court trending significantly to the right in recent years, with even its left flank being relatively middle-of-the-road, relative to history.
(We should note that in the charts below, the zero point is arbitrary. Thus, it's better to compare the justices to each other and to the Supreme Court's past membership.)
The court's five more conservative justices, meanwhile, are clearly right-of-center, with four of them (Clarence Thomas, Antonin Scalia, Samuel Alito and John Roberts) being among the most conservative justices since 1935. This suggests the court has a clear conservative majority in addition to a left wing that isn't all that left-wing.
But not everybody agrees. Another measure of the ideology of the Supreme Court justices comes from Michael A. Bailey of Georgetown University.
While Bailey shows the court has become significantly more conservative since, for example, the 1960s, he still pegs the four more liberal justices as clearly to the left of the court, historically speaking.
In addition, Bailey's model actually suggests the court, while more conservative than in most of the last several decades, isn't all that much more so than it was in the 1970s or when Sandra Day O'Connor was the swing vote in the 1990s and early 2000s. He also shows the left wing not moving to the middle but getting more liberal.
What both of them agree on, though, is that swing vote. In both charts, the swing vote is denoted by the yellow line. And according to both measures, that swing vote, with the exception of the 1960s, has been consistently a little to the right of center.