I'll join a couple of dots here ... Rush just threw out there that maybe the foreign actors being listened to were carefully chosen given the likelihood that they would be talking to certain known US persons (that way you "incidentally" get to listen to those
targeted US persons by a backdoor means). After all, getting FISA clearance for listening to "foreigners" is a trivial task.
So, how do you compile your list of foreigners? Well, Clapper's vast trove of metadata (who calls whom) gives you a nice concise list with little effort.
Aren't the dots joining up nicely here?