The not-so-veiled threat made by Florida Rep. Matt Gaetz to Michael Cohen in a tweet earlier this month—“Do your wife & father-in-law know about your girlfriends? Maybe tonight would be a good time for that chat. I wonder if she’ll remain faithful when you’re in prison. She’s about to learn a lot.”—created an uproar and ultimately an apology of sorts. Whether the congressman’s words were meant to intimidate is a political and legal question, one intertwined with issues of intent and the protections granted by the Constitution’s speech and debate clause. But whether the cheating is pertinent depends on evidence law.

In a trial, or in a Congressional hearing, it is fair to test a witness’ credibility. Congress has no rules of evidence—but those applied at trial are informative and help the discussion of whether Cohen’s having girlfriends while married is fair game.