If it isn't, Breitbart has opened himself up to a defamation judgment.
The extent McGinniss and Random House are at risk depends on how they couch the material, in the book. If the book says "there are rumors ..." then it's not defamatory.
If it is defamatory, Palin can just hire a lawyer on contingency, and let the case ride out without much investment the way of personal time or emotion.
I Agee! Breibart would not have released this if he didn’t think this was legit! Many MSM people are after to get him for all of the other scandals he broke, he’s not going to open himself up to the media sharks if he can’t back this up
Not necessarily. Defamation can occur by way of innuendo. Uncritically repeating a rumor makes you a "publisher" of that defamatory innuendo and puts you on the hook for a potential claim, depending on what the plaintiff wants to do with you and then on how well your facts match the legal requirements. Judges and juries will generally not be fooled by the thin disguise of "just repeating a rumor," especially when you've got the smoking gun required for a successful NYT Malice case, as appears to be the case here.
Strategically, BTW, Palin can have it both ways if she wants. Run the race without filing suit, then after she either wins or loses, the statute of limitations (most likely 2 years, depending on the state in which the case is brought) will not have run out by November 2012, and she will be free to bring suit without doing damage to her 2012 political efforts.
This could turn McGuinness/Random House into Sarah Palin's biggest donors. Sweet justice.