Guy Benson
I thought for sure she'd sit this one out, given Castle's sizable lead over Coons, and O'Donnell's personal and political liabilities.  Nope: Sarah Palin waded into the Delaware Senate knife fight and endorsed Christine O'Donnell for Senate on Sean Hannity's radio show this afternoon, then confirmed it with a facebook post this evening:
Please support Christine O’Donnell in Delaware. She will support efforts for America’s energy security, patient-centered health care reform, cutting government waste, and letting the private sector thrive and prosper! We can’t afford “more of the same” in Washington. Christine will help usher in the real change we need to get America on the right track. Please visit her website at www.christine2010.com and follow her on Facebook and Twitter.
Some commenters are getting combative over Palin's decision, and the Castle camp is coming out swingin' (via Dave Weigel):
Tuesday's primary will be decided by grassroots Republican voters here in Delaware, not out-of-state interest groups who are working to control the outcome.  Mike Castle has overwhelming support from from respected conservative Delawareans, including former Gov. Pete DuPont and Judge Bill Lee, who know that Castle is the true fiscal conservative and the only candidate who can win this seat for Republicans in November.
Castle's campaign didn't stop there; they've filed an Federal Election Commission complaint against O'Donnell alleging an "illegal scheme" to coordinate fundraising efforts with the Tea Party Express. 

This smells a little desperate to me.  The word 'overkill' comes to mind, but after what happened in Alaska, it appears Team Castle is taking no chances.

Meanwhile, a group of conservatives is hosting a radiothon for O'Donnell in Delaware tonight, which will almost certainly get a boost from the Palin nod.  Jim Geraghty tweets that today has been--by far--the best day the O'Donnell campaign has had in weeks, maybe ever.  But will they have an even better day next Tuesday?  If not, will O'Donnell bow out gracefully, or pull a Murkowski?

Guy Benson

Guy Benson is Townhall.com's Senior Political Editor. Follow him on Twitter @guypbenson.

Author Photo credit: Jensen Sutta Photography