Having litigated libel suits, I can tell you that it would be fantastic if John Kerry filed a libel suit against these people. First, he would be obligated to testify at a deposition, and we could have all kinds of fun with that. Second, in a libel suit, the measure of damages is based on the harm to a person's reputation, and so Kerry's reputation would be relevant. You could get into all kinds of events from his life, and depose all kinds of witnesses, while delving into that issue.
I was mulling some of the principles myself: truth being a defense, public figure. Wondering, frankly, if Kerry can't sue as a public figure (absent malice - no, not that kind), how can he or his agents sue a third party who doesn't represent the ad as theirs or who add a disclaimer? I haven't litigated libel so.....
But with regard to the tactic being used, surely those of us with some legal training and experience can step up to the plate and offer these guys some help, hey?
Then being a lawyer you know that the primary reason for this is to give liberal station managers cover to refuse to air this "controversial ad" and th bully others into not doing it. Even if he DID file a suit, the only purpose would be to get an injunction until after the election to prevent them from airing it.