It's been a while since I've read up on this, but my understanding is that the NSA vacuums up everything it can and operates under the rather creative legal the

It's been a while since I've read up on this, but my understanding is that the NSA vacuums up everything it can and operates under the rather creative legal theory that this doesn't count as "collection" until it's returned by the search engine, which they pinky-promise won't return it unless their prediction model is at least 51% sure that it's a foreign communication.