Democrats are thrilled that tea party-backed candidate Christine O'Donnell won Tuesday's GOP primary in Delaware. That's because Democrats were sure to lose the Senate seat formerly held by Vice President Joe Biden if Rep. Mike Castle, R-Del., had won the primary. But now Democratic candidate Chris Coons is the heavy favorite to defeat O'Donnell, who has a history of financial problems and strange behavior. Whether Democrats retain this seat could determine whether they keep or lose control of the Senate. That's why the Wall Street Journal editorial board, National Review, the Weekly Standard and other conservative groups backed Castle.