Anyway, can we stop with the claims only that the liberals/Democrat are applying a litmus test? The simple fact is, both sides are. Each side looks for what it believes to be true in the candidate, and each side sees what it doesn't feel to be true as a drawback. For perfect proof of this, check out all the rhetoric coming from the religious right about abortion being the key battle - you're telling me they don't have a litmus test?
Both sides do, if for no other basis than judicial activism v. judicial restraint. So both sides are guilty.