Comment by sdoowpilihp

That is where plausible deniability comes in to play. He could lie under oath, and it's still plausible that he is telling the truth.

The only play on the government's part at that point, as far as I can tell, would be to acknowledge that the NSL did exist in order to prove that he was lying. They likely would not do this though, as it defeats the purpose of the gag order.