See last night’s post for some back-of-the-envelope math on his chances. This is actually … good news for O’Donnell, isn’t it?

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…

The GOP source did not have specifics on when Castle’s team would conduct the poll, but viewed it as a practical step even if the nine-term congressman was unlikely to re-enter the race…

Delaware GOP National Committeewoman Priscilla Rakestraw said she has fielded dozens of calls over the last 48 hours, mostly from Democrats, about a potential Castle write-in campaign.

“They want to organize a write-in campaign. I’m stunned. Obviously, they don’t like their option of voting for Chris Coons. I pass them along to Mike Castle’s organization. I think they are waiting for a nod from Castle,” Rakestraw said.

Castle’s team won’t confirm that they’re polling, but why wouldn’t they do it? Surely his name recognition’s high enough in the state that they’d want to know if he has a shot to win. Here’s the irony: If you think O’Donnell’s numbers against Coons are already so grim that she stands no real chance of winning — and most O’D supporters do not think that — then it’s a no-brainer that you should want Castle in the race. Worst-case scenario is that he and O’Donnell split Republicans and Coons manages to hold onto enough Democrats to squeak to victory, but then a Coons victory is how things look at the moment anyway. Bad-case scenario is that Castle manages to pull enough Dems from Coons and Republicans from O’Donnell to win the seat himself, in which case the GOP is a step closer to a Senate majority. Best-case scenario, obviously, is that Castle and Coons split the Dems and O’Donnell squeaks through on the strength of conservative supporter. If, however, you think O’D can still beat Coons head-to-head — and especially if you’re a DeMint-ian “true conservative” who regards centrist Republicans as even worse for conservatism than Democratic victories — then you should probably want Castle to stay out. “Anyone but the RINO,” no?

Another grand irony here? Castle’s hard feelings towards O’Donnell and the base may be so hard that if he polls this and the numbers show that he’ll hurt Coons more than he’ll hurt her, maybe he’ll decide not to run just to spite her. RINO revenge?