Isn't this just a name-recognition thing?
Yes.
Not really. There isn't anyone on that list who isn't familiar to most serious Republicans who will vote in the primaries.
False. Most primary voters, though they are certainly more familiar with the bench than the average citizen, still aren't up on every possibility. You really think most people have actually heard of Charlie Crist? The "No Opinion" category is so large for those guys not because people are ambivalent, it's because they've never heard of them.
