Christie performs like Generic Republican right now, voters know little about him. Clinton OTOH is one of the best known people not only in the US but the entire world. On paper he seems impressive but let's wait and see until he actually hits the trail.
Actually he performs way better than Generic Republican. Generic Republican would not be leading Hillary in PA.
That said, Christie is riding high right now. Just coming off the glowing media coverage of his landslide victory just over the border. I live in SE PA so I saw tons of his ads. However, the Tea Party is going to take their pounds of flesh off him during the primary (no pun intended...really). Even if he does make it out of the primary, which is not even close to a certainty, he'll be heavily damaged from the right-wing attacks as the Tea Party despises him.
