It seems to me that Vindman's testimony as it relates to Solomon's reporting is cut and dry slander. Vindman was under oath to tell the truth and he asserted as a fact that Solomon's reporting was untruthful. Now Solomon has responded with a point by point, well sourced, refutation of Vindman's assertion, it's clear that Vindman's assertion was defamatory. Congressional witnesses do not enjoy the protections from defamation lawsuits based on their testimony that Congressmen do, so Vindman is a ripe target for a defamation lawsuit if Solomon is interested.