IAA(lso)NAL, but libel or slander typically requires it to be willful or maliciously, and truthfulness is an affirmative defense in the US, I believe.
It would be virtually impossible to prove that he didn’t really believe this was true and that he did it solely out of malice. While it’s obvious in cases like the election conspiracies that there was a willful disregard for the truth, in this case he just has a very poor legal argument.
