Again, I'm not privy to how the United States runs its security program, but my understanding is that it's not just to see who's an immediate threat, but to try to prevent threats by looking at patterns of people who may be overflying the United States. For example, one thing that seems to come out is that before someone does something drastic, they make several dry runs at it to check out the defence system. So I think the wish to identify those flying over their airspace is related to that, to see how to prevent those studying what they can do to attack American national security from the air.
