Maybe not. He hasn't exactly set the house of fire in the Senate and could be seen as part of the Ancien Régime in 2012.
Not to mention I read a PPP poll recently which said that a higher number of voters disapprove of his performance then approve. And even though I can't remember the exact numbers they were moderately higher then the approves, so Casey could be vulnerable with the right candidate.
Plus Casey campaigned and ran as a moderate and his votes in the Senate have been anything but which in a state like Pennsylvania also counts as a mark against him.