[OneWingedShark]

So, the government gets around that by saying the NSA is not an investigating body. It merely gathers information. The investigators still need a warrant, but once they have the warrant, they can access the NSA database.

The problem with that rationale is that using it they have a "information-gathering" crew could go into your house collect everything, have the investigation-crew talk to people and then have "suspicion of reasonable cause" wherewith to get a warrant and go through your things.

No good will come of this.

[Cboldt]

The only way it plays out is in court, usually on criminal charges. The judges then are pretty good about tossing evidence obtained without a warrant.

So, the practice of over-sampling (if you will) has no downside risk. None. The bootstrapping issue you raise doesn't exist for the investigators. They have to have suspicion before they can access your NSA file, and armed with suspicion, they can easily get a warrant.