Here is an interesting thing to think about which country spies on Americans the most and how? Are there New Zealand commandos sneaking around the shores tapping cables? Moles working in the AT&T for the Canadian government? What happens if one of those individuals get caught, are they quietly allowed to leave, and if they commit any crimes do the charges get erased magically? Otherwise, if that doesn't happen there is danger they'll grab our spies in their countries in turn. Or they just blatantly pass lists around of who works for whom so they don't interfere with each other as that would preclude getting the data back through the loop to the NSA.
There is of course another loophole and that is private entities collecting data. The Constitution doesn't say anything about that, so the government figures it's fare game if they just pay a company to collect the data and then they query later. They didn't collect it so it's not "spying".