Public figures, especially elected officials, have a significantly
reduced protections from defamation in the US.
Not only is truth an absolute defense to defamation in the US, the plaintiff must show that the defendant's statements were made with actual malice if the plaintiff is a public official. Merely being unsure if something is true or being negligent in determining the truth of it is not sufficient.
Furthermore, nearly all civil lawsuits require that actual damages be done in order to have standing at all. That is, you need a dollar amount because that's basically the only remedy that a civil court can make. That means that if the damage is due to lost reputation and your reputation has already been thoroughly soiled, it will be incredibly difficult to put a dollar amount to it.
So:
1. It has to be actually false as shown by the plaintiff
2. It has to be known by the defendant to be false as shown by the plaintiff
3. It has to be made intentionally to harm the subject as shown by the plaintiff
4. The statements must have actually harmed the subject in monetary terms as shown by the plaintiff