A plain reading of the Fourth Amendment clearly prohibits this sort of mass surveillance. Constitutional arguments tend to degenerate into semantic ones, so let

A plain reading of the Fourth Amendment clearly prohibits this sort of mass surveillance. Constitutional arguments tend to degenerate into semantic ones, so let's ignore that argument for now. The threat to privacy and democracy is that anyone with access to this data can blackmail anyone. The NSA is storing as much data as possible for as long as possible. This means they have the communications (metadata or otherwise) of every potential politician, and thus the ability to blackmail them to distort their decisions. We're told that there are safeguards in place to prevent such abuse, but those safeguards are secret, and I can't imagine any safeguards being foolproof. The best safeguard to protect our democracy is to not allow such a system to be built.