Litmus test

Schieffer brought up, very directly, the issue of abortion, Roe v. Wade, and the Supreme Court. McCain answered first:

SCHIEFFER: All right. Let's stop there and go to another question. And this one goes to Senator McCain. Senator McCain, you believe Roe v. Wade should be overturned. Senator Obama, you believe it shouldn't. Could either of you ever nominate someone to the Supreme Court who disagrees with you on this issue? Senator McCain?
MCCAIN: I would never and have never in all the years I've been there imposed a litmus test on any nominee to the court. That's not appropriate to do.
SCHIEFFER: But you don't want Roe v. Wade to be overturned?
MCCAIN: I thought it was a bad decision. I think there were a lot of decisions that were bad. I think that decisions should rest in the hands of the states. I'm a federalist. And I believe strongly that we should have nominees to the United States Supreme Court based on their qualifications rather than any litmus test.

Now, I am sure that if Obama were asked the question first, he too would have made this weird distinction between a litmus test and qualifications. Wtf is the difference? This topic comes up every time there's a new nominee to the court, and everyone agrees that we shouldn't have litmus tests and is on the lookout for people who are hiding their litmus-testing intentions.

As far as I can tell, a "litmus test" means "someone's thoughts on a specific court case, either in the past or potentially pending." "Qualifications" means "someone's judgement on..." well, it is not clear on what basis their judgement should be judged on, since judging them on judicial cases would be too litmusy. Perhaps he vetting administration should ask them logic questions? Time them on Sodoku?