That’s defamation. Sue his butt.
Any member of Congress or the Senate may make ANY kind of slander or defamation from the floor of the legislative chamber to which he or she belongs, and not be held accountable in any court in the land. The caveat here is that it must first be publicly spoken from the floor of the chamber, then any repetitions later are equally immune to prosecution. This is an old rule inherited from the English Parliament, relating to the fact that a member of the House of Commons or the House of Lords could criticize the King, and suffer no consequence from the Crown.