I thought the place to start would be some parameters.
Christine O'Donnell got 17.4% (2505 votes) in the 2006 3 -way primary in which she placed third. She was not the organization endorsed candidate and was outspent.
In 2008 as the GOP nominee for Senate, she lost to incumbent Senator Joe Biden ,but her losing margin was not outside the range of other statewide Republicans who lost. She received 35.3 % to Ins Commissioner candidate John Brady's 41.0%,Presidential candidate John McCain's 36.9 %. GOP Governor candidate Bill Lee's 32.0 % and GOP Lt. Gov candidate Charlie Copeland's 38.7%. While she was trounced in New Castle County along with her ballot mates except Mike Castle, she lost closer than Lee & Copeland in Sussex County where she only lost by 272 votes of 86,518 cast countywide. She lost Kent by a smaller margin than Bill Lee,who was making his third bid for the office of governor.
O'Donnell is once again in a statewide primary in which she is not the organization endorsed candidate and it is likely she will be outspent.I am assuming that since she has run twice statewide, has more name recognition and shown some visible support downstate she will get in 2010 at least the 17.4% she received in 2006.
Jan Ting, a Republican party regional leader who had never before held elected office, won the 2006 primary with 42.5% of the vote (6110 votes). Ting ran as the organization endorsed candidate. I am assuming that U.S. Rep Mike Castle, who is the organization endorsed candidate in 2010, has held statewide elected office since 1980 and has a much larger campaugn fund than O'Donnell, will do at least as well as Jan Ting and will get at least 42.5% of the vote.
My contention is Castle and O'Donnell are fighting over the 40.1% of the vote (5771 in 2006) that Mike Protack received and whatever new primary voters each side can bring out.
If this theory is remotely accurate, Castle can lose 4 of 5 former Protack voters (thereby getting only 8 of the 40% that Protack had gotten in 2006) and still get more than 50% of the overall vote. Since there is no guarantee that O'Donnell was the second choice of the majority of Protack's voters, she definitely has an uphill fight. It is also possible that some of Protack's strongest supporters may stay home rather than voter for either of them , a scenario which I think benefits Castle since it would tough to generalize Protack's supporters as reliable supporters of the Republican statewide organization.
2006 Delaware statewide primary results:
2008 statewide general election results by subdivision: