I don't have much say regarding the winner & loser in DE, other than I hope that Castle would do the right thing now for the party and support O'Donnell.
That being said, looking at the numbers from http://elections.delaware.gov/results/html/election.shtml
Total Repub votes for the Senate primary: 57,582
Total Dem votes for DE State Treasurer (one of two D primaries): 34,721
If O'Donnell can keep the momentum, and the R base can stay fired up....yeah, its an extreme longshot