This is true, but his reasoning as applied to Flynn is so dubious that it’s become chum for a feeding frenzy among lawyers on Twitter today. Dershowitz’s point is straightforward: It’s only a crime to lie to a federal agent if you lie about material fact. If the sky is blue and you tell the FBI it’s red, there’s no jail time for that because that fact isn’t material to whatever it is they’re investigating.

But the question of which facts are “material” isn’t always clear cut. How to define them? Well, says Dershowitz, here’s one way: If the feds already know the fact before you mention it, then it can’t be material. Your lie hasn’t misled them. They won’t waste any time or money investigating it. They already know the truth. No harm, no foul, no prison. In fact, if the feds are asking you a question about a fact they already know, presumably they’re only doing it in hopes that you’ll perjure yourself, right? That’s the Flynn situation, Dershowitz argues today in an op-ed.

Flynn, during his brief time as national security adviser to President Trump, told FBI agents untruths that are contradicted by hard evidence. Why he did that remains a mystery because, with his vast experience in intelligence gathering, he must have known that the FBI had hard evidence of the conversations he denied having with a Russian diplomat. Be that as it may, this reality does not automatically exclude the possibility that the FBI acted improperly in eliciting untruths from him.

The FBI knew the truth. They had recordings of the conversations. Then why did they ask him whether he had those conversations? Obviously, not to learn whether he had them but, rather, to give him the opportunity to lie under oath so that they could squeeze him to provide incriminating information against President Trump.