Has more to do with being a public figure. Defamation is nigh unto impossible to win once your name is out there as part of the public discourse. Free speech issue. About the only realistic recourse is more free speech, I.e., Ayers putting out articles and interviews in an attempt to rehabilitate his reputation.
Wouldn’t you agree his “brand” was improved with his core audience by his mention from Sarah Palin, and is not in need of “rehabilitating?” For Bill Ayers to claim any kind of damage is laughable.