(My guess is that he won't do it. Even though Coons was losing to Castle he was still getting 42-45 percent against him. I think Coons has made a good impression and even if Castle got in if Coons can get 40%, O'Donnell will get at least a hard cord 25% and Castle would at best get in the mid-30's--and that's a big chore if you're running as a write-in):
Will it be another case of a sore loser trying to win a Senate seat after voters already rejected him in the primary? Or will it be a declaration by the moderate wing of the Republican Party that enough is enough with these Tea Party folks?
Whatever it is, it looks like Rep. Mike Castle (R-Del.), his all-but-assured trip to the Senate derailed in the Sept. 14 primary by evangelical upstart Christine O'Donnell, is seriously considering continuing his campaign by waging a write-in effort. It is the same strategy being waged in Alaska by Sen. Lisa Murkowski, who unexpectedly lost her primary battle with a Tea Party candidate.
Castle has been a political giant in Delaware since his first election to the state Legislature in 1966. Elected lt. gov. and then two terms as governor, he has won nine terms as the state's only member of the House; in the Democratic year of 2008, with Joe Biden on the ballot as a candidate for the Senate and vice president, Castle nonetheless received 61 percent of the vote
Mike Castle has until Sept. 30 to decide what he will do.
http://www.npr.org/blogs/itsallpolitics/2010/09/26/130143905/delaware-s-mike-castle-considering-write-in-effort-to-save-senate-seat“I don’t want to necessarily interfere with Republican chances,” said Castle, although he added, “I’ve had a lot of people approach me about it.”…
Asked directly whether he was considering a bid, Castle said: “I’ve given it some thought. I probably won’t do it…. I’m not exactly approaching this with bated breath.” Castle spokeswoman Kate Dickens said the congressman has had conversations about a write-in effort but that he likely won’t pull the trigger.
“We are getting a lot of mail and calls on it,” Dickens told POLITICO. But she said the likelihood of Castle mounting a campaign was still, “under 5 percent.”
http://hotair.com/archives/2010/09/22/here-we-go-mike-castle-hints-at-write-in-campaign-in-delaware/