People, Toomey (a good candidate) won by 2 points against Sestak (not a bad candidate, but he barely won the primary running as a left-wing democrat) in 2010.
Do you really believe that casey (a moderate incumbent) is just barely edging Smith, a mediocre, tea party member candidate? I think PPP poll with Casey leading by 11 is closer to the Real World.
And I know Sestak campaigned while Casey hasn't campaigned at all, but, still, 2010 was a very republican year. I don't buy this poll.
But Sestak was a very appealing candidate personally and had people fired up/ran an incredible campaign. Plus, Toomey was a good candidate and ran a flawless campaign but Sestak hit him hard on his negatives.
That said, yes, you're right: Casey is still favored but this has become a race now. That's the point. This was always supposed to be a guaranteed win for the Dems, one of those "We definitely don't have to worry about spending time, money, energy there" types of race. That's not the case.
By the way, see my PA 2012 thread to see why the news got even worse for Casey today. That's perhaps the biggest story of the day...