As I read it, Coffee260 was simply reporting on what he heard on a radio show from some talk show host.
Disredarding the constitutional issues, I don’t see how someone can be legally liable for repeating what he hears on the air.
I think this letter from legal counsel is an impermissable intimidation against all legal ethics.
See the Powerline post.
Repeating a libel second hand is no defense, if you had reason to believe the libel false or if you act with reckless disregard for the truth. Coffee260 simply repeated what he heard (and a confirming email) and presented it "for what it was worth". FR has enough fact checkers to get to bottom of the matter if Dean and Siebelius have alternative explanations.
Seibelius representations about the state of the Kansas National Guard are so at variance with the facts that it naturally brings her motives into question.