What the NSA is not supposed to know is who we are, assuming that you, like me, are a U.S. citizen. The identities of Americans swept up in surveillance of foreign nationals are supposed to be kept hidden (“masked,” as the vernacular has it) unless there’s an intelligence need to figure out who we are. That’s the mystery of the Tucker Carlson situation. Did someone in the government alert Carlson that his communications had been intercepted? And, if so, how and why did they know?