Delaware's Republican Governor Mike Castle was supposed to have the Senate race all sewn up. But heading into a Tuesday night primary, Public Policy Polling says Tea Party-backed and Palin-endorsed conservative Christine O'Donnell actually has a three-point lead. That's within the margin of error, but enough to get major attention: O'Donnell is widely considered far less electable than Castle in the general election. Politics bloggers are all over this news:

• 'Trainwreck a'Comin,' says Josh Marshall of Talking Points Memo. Delaware has been "totally dominated for most of the last three or four decades by three or four guys who keep getting reelected, except when they trade one of the state's four major offices and get elected again." This could be a major upset--and after a similar upset in Alaska following a Palin endorsement, it just seems possible. Also, he's of the opinion that Christine O'Donnell is pretty nuts:

She's the one who says it's not enough to be abstinent. You have to eliminate sexual desire entirely. Which suggests she's what you'd call an aspirational politician rather than a realist.

• Doomed in the General Election  James Joyner at Outside the Beltway agrees with Marshall: "If PPP's numbers are right, O'Donnell wins this thing. And she's completely unelectable outside the confines of a small turnout primary competition."

• GOP Tried, Failed to Stop This  "O'Donnell's surge," judges Salon's Steve Kornacki, "is all the more remarkable because Castle and the GOP establishment recognized that it was possible--and tried to nip it in the bud." That didn't work. Of course, he adds, "it's possible that Castle will still survive." The lead is a "slim" one, and "given the tiny Republican primary universe in Delaware, there's probably a lot of wiggle room in those numbers." But it's possible the Tea Party will "triumph," and also that Delaware won't be their only win:

Another new poll released on Sunday, also from Public Policy polling, finds that Ovide Lamontagne, a grassroots conservative favorite, is now trailing the establishment-backed Kelly Ayotte by just 7 points in New Hampshire's GOP Senate primary.

• Conservatives: Vote Castle!  "William F. Buckley, the godfather of the modern conservative movement," writes Mark Hemingway at The Washington Examiner, "had some simple advice for what to do on Election Day: Vote for the most conservative candidate that is electable." He judges that Castle, a "liberal Republican," is still better to have in office than a "liberal Democrat," who may win if O'Donnell gets the nomination. He also calls O'Donnell's recent campaign "erratic and dishonest," referring, among other incidents to "an Internet video" posted by O'Donnell aides "baselessly alleging that Castle had a gay affair." The Weekly Standard is also turning out fairly anti-O'Donnell, with John McCormack writing up a story on O'Donnell "falsely impl[ying] she was taking master's degree classes at Princeton." Meanwhile, his colleague Jay Cost shares Hemingway's view on how conservatives should vote:
  

I share the concern of many that Castle is a moderate whose loyalty to GOP causes will be questionable. Even so, that concern has to be balanced against the question of O'Donnell’s electability.

• Conservatives: Vote Conservative!  That's Robert Stacy McCain's response at The American Spectator. He thinks Republican concern over O'Donnell might be misplaced: