Truth is Defense

A public official may sue for defamation, but to prevail they must establish that the defamatory statement was made with actual malice. That is, the public official must prove by clear and convincing evidence that the defendant made the alleged defamatory statement with actual malice - either with knowledge that the statement was false or with reckless disregard as to the truth of the statement.
A conditional constitutional privilege based on First Amendment considerations for those who make written or oral statements concerning public officials was established by the Court. Within the terms of that conditional privilege, statements concerning a public official, even if proven to be false, would not be the basis of civil liability unless actual malice—i.e., actual knowledge that the statement was false or a reckless disregard for whether the statement was false or not—was shown.
A true statement is the ultimate defense to any action for libel or slander. It is not necessary for the defendant to prove the literal truth of the precise statement, and slight inaccuracies in the statement published are immaterial to the success of the defense. Nor is it necessary to prove that the statement was true in every particular. All that is necessary to establish the defense of truth is that the matter was substantially true.