Stephen Henderson, Deputy Editorial Page Editor of the Detroit Free Press, writes in to note that Barack Obama gave a fairly detailed answer a few weeks ago to the Free Press editorial team on the question of what kind of Supreme Court Justice he would want to appoint:

Q: You voted against confirming both Justice Alito and Chief Justice Roberts (for the U.S. Supreme Court). You said you want justices who are passionate. ... You taught constitutional law for 10 years, so I'm wondering if you can tell us, outside the context of the current court, what justices would you use as models for your pick?

A: Well, it depends on how far you go back. I mean, Justice (John) Marshall was pretty good ... but those were some different times. There were a lot of justices on the Warren Court who were heroes of mine ... Warren himself, Brennan, (Thurgood) Marshall. But that doesn't necessarily mean that I think their judicial philosophy is appropriate for today.
  Generally, the court is institutionally conservative. And what I mean by that is, it's not that often that the court gets out way ahead of public opinion. The Warren Court was one of those moments when, because of the particular challenge of segregation, they needed to break out of conventional wisdom because the political process didn't give an avenue for minorities and African Americans to exercise their political power to solve their problems. So the court had to step in and break that logjam.
  I'm not sure that you need that. In fact, I would be troubled if you had that same kind of activism in circumstances today. ... So when I think about the kinds of judges who are needed today, it goes back to the point I was making about common sense and pragmatism as opposed to ideology.
  I think that Justice Souter, who was a Republican appointee, Justice Breyer, a Democratic appointee, are very sensible judges. They take a look at the facts and they try to figure out: How does the Constitution apply to these facts? They believe in fidelity to the text of the Constitution, but they also think you have to look at what is going on around you and not just ignore real life.
  That, I think is the kind of justice that I'm looking for -- somebody who respects the law, doesn't think that they should be making law ... but also has a sense of what's happening in the real world and recognizes that one of the roles of the courts is to protect people who don't have a voice.
  That's the special role of that institution. The vulnerable, the minority, the outcast, the person with the unpopular idea, the journalist who is shaking things up. That's inherently the role of the court. And if somebody doesn't appreciate that role, then I don't think they are going to make a very good justice.