It's not much of a defamation case
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I'm no lawyer, but it seems that there is a very good case.
The legal definition is any intentional false communication, either written or spoken, that harms a person's reputation; decreases the respect, regard, or confidence in which a person is held; or induces disparaging, hostile, or disagreeable opinions or feelings against a person.
In New York Times v. Sullivan the Supreme Court balanced the plaintiff's (a policeman) interest in preserving his reputation against the public's interest in freedom of expression in the area of political debate. It held that a public official alleging libel must prove actual malice in order to recover damages. The Court declared that the first amendment protects open and robust debate on public issues even when such debate includes "vehement, caustic, unpleasantly sharp attacks on government and public officials."
A public official or other plaintiff who has voluntarily assumed a position in the public eye must prove that defamatory statements were made with knowledge that they were false or with reckless disregard of whether they were false.
defamation (of character)
n. the act of making untrue statements about another which damages his/her reputation. If the defamatory statement is printed or broadcast over the media it is libel and, if only oral, it is slander. Public figures, including officeholders and candidates have to show that the defamation was made with malicious intent and was not just fair comment. Damages for slander may be limited to actual (special) damages unless there is malice. Some statements such as an accusation of having committed a crime, having a feared disease, or being unable to perform one's occupation are called libel per se or slander and can more easily lead to large money awards in court and even punitive damage recovery by the person harmed. Most states provide for a demand for a printed retraction of defamation and only allow a lawsuit if there is no such admission of error.