Politico reports that Rep. Mike Castle is considering running as a write-in candidate:

Rep. Mike Castle is planning on polling a potential three-way Senate race to test his chances as a write-in candidate, a Delaware Republican tells POLITICO.

Castle, who lost his GOP primary by a 6-point margin to tea party upstart Christine O’Donnell nine days ago, opened the door to a potential write-in bid Wednesday evening when he told reporters off the House floor it was still a possibility he was considering. …

A spokeswoman for Castle, who put the chances of him running as a write-in “under 5 percent,” said her boss likely wouldn’t settle on a final decision before next week. According to the state Elections Commission, Castle would have to complete a form by next Thursday to officially qualify as a write-in candidate.

When Battle ‘10 spoke to a campaign spokesman about the rumors yesterday, he said, “The campaign is not speculating on speculation, we’ll wait until Mr. Castle makes a decision.”

Analyst Nate Silver made a model of the three-way race Castle’s write-in candidacy would cause, and predicted these results: Coons winning with 37 percent, Castle next at 34 percent, and O’Donnell finishing last with 29 percent. He also speculated that Castle entering the race could improve O’Donnell’s chances of winning — since he thinks that (a) Castle is more likely to appeal to Coons voters and (b) that it’s unlikely that O’Donnell will capture more than about 30 percent of the vote.

Other updates on the Delaware race:

● Before he was a “bearded Marxist,” Democrat candidate Chris Coons was a Ronald Reagan campaigner and the founder of Amherst College Republicans.

● Talking Points Memo reports on how Christine O’Donnell worked in 2008 to raise media awareness of coma victim Lauren Richardson. Ms. Richardson’s mother was trying to remove her daughter’s feeding tube, while her father was trying to keep her alive. The parents eventually agreed to keep the feeding tube in place, and now both help take care of Ms. Richardson.

● Biden will be attending a Coons fundraiser in Florida Friday. Will the gaffe-prone vice president top Reid’s awkward endorsement of Coons as “my pet”?

● On Hannity last night, Karl Rove praises O’Donnell, says she’s “on the right course,” even though he remains concerned about how polls show her 15, 16 points behind Coons.

Watch the video (begins about 5 minute mark):