I didn’t hear it happen, but evidently she did it this afternoon on Hannity’s radio show. No audio (yet), alas, but here’s Hannity’s tweet:

Thanks @SarahPalinUSA for the last minute call in. Endorsement of Christine O’Donnell was an exclusive. Said she hadn’t told Christine yet.

And here’s Dave Weigel, who’s relishing the thought of a Palin vs. the Weekly Standard primary battle, with some background:

I previously reported that O’Donnell met with Palin at the August 28 “Restoring Honor” rally in Washington. Here’s some more of the backstory. Matt Moran, O’Donnell’s campaign manager, previously worked with Doug Hoffman’s campaign in NY-23. It was Palin’s endorsement of Hoffman that really rocketed him into the stratosphere, and made her endorsement valuable — something that was not at all clear in October 2009, when she took that first leap. And Moran’s connection to the Palin camp was obviously helpful in keeping the possibility of an Palin-O’Donnell endorsement alive, even as Republicans tried to stunt her momentum and prevent any more groups like the Tea Party Express from jumping in.

Guy Benson wonders how valuable this endorsement really is given that hardcore Palin fans were already surely planning to vote for O’Donnell next week. The value, I think, is purely in the buzz it’ll generate, which will catch the attention of conservatives who aren’t necessarily hardcore Palin fans but also, until now, weren’t paying close attention to the race. High turnout among righties is Castle’s biggest nightmare and this can only help in that regard. Having said that, I’m surprised that she jumped in. I joked last week in one of the Castle/O’Donnell posts that Sarahcuda might join Chris Christie in endorsing the RINO and a commenter argued that, whatever happens, she stands to gain little by endorsing O’Donnell. Which is true: Either Castle wins anyway and the media runs with its predictable “Palin’s influence overrated!” storyline or O’Donnell pulls the upset and the media runs with a “did Palin just hand a Senate seat to the Democrats?” storyline. Only if O’Donnell beats Coons in November does Palin stand to win big here, and I’m still extremely skeptical of that happening. Even with conservatives energized by an O’Donnell win, the Democrats will be frantic to take advantage of Castle’s defeat and hold this seat; the November bloodbath will be so terrible for them that control of the Senate may hinge on it, which means they’ll hit O’Donnell with everything they’ve got. In fact, since it’s a blue state, it’s an ironclad guarantee that they’ll use Sarahcuda’s endorsement of her to motivate their own Palin-hating base voters to turn out.

As of last night, Jim DeMint’s group hadn’t endorsed O’Donnell; it’ll be interesting to see if this opens the floodgates for other “true conservatives” or if electability trumps. Exit question: The primary’s just four days away. Is Palin too late or right on time?

Update: Here’s the audio. She mentions O’Donnell’s opposition to cap and trade and ObamaCare as evidence that she’s the conservative in the race. Fair enough on the first point — Castle did vote for C&T in the House — but he voted against O-Care. The only concession he’s made on that that I’m aware of is that the GOP can’t repeal it over the next two years with Obama’s veto pen still a threat. Click the image to listen.