As well as? In 2008 Castle won with 61% of the vote, absolutely destroying his Obama-endorsed opponent. 56 Republicans ran for office in DE in 2008, O'Donnell had the 45th best showing among them.
May I ask a question (actually two)?:
Do you live in Delaware?
If not, why are you arguing against the judgment of the Delaware voters?
If so, do you prefer O'Donnell or Coons to be your Senator? Because those are the only choices available.
Gee, I wonder why Castle did so well in a Obama election?