Ok, did alot of reading relative to the NSA's program of intercepting communications without warrants on behalf of the President. This is simple.
- The NSA obviously intercepts a lot of communications 'data', some of which makes it across the water to the US, or from here to there. That falls under Article II of the Constitution. The Executive Branch has the right ( and the requirement) to conduct this kind of 'warrantless' survellience against foreign entities, be they countries or terrorist organizations, outside and inside our borders.
- They may know who is sending or receiving the information (Al Qaeda operatives, etc.), but may not know initially who's on the other end, sending or receiving.
- If the initially unknown person winds up being a US person (citizen or resident alien), THEN we need to deal with the Fourth Amendment. If they're not a US person, all bets are off.