[hiram112]

Under Article I, Section 8, Congress has the power to declare war, raise and support Armies, provide and maintain a Navy, and organize, arm, discipline, and call forth a militia.

Using spies (human intelligence) is as basic to warfare and defense as any other weapon.

Spying on citizens is where things get murky.

And as much as many readers here may dislike the intelligence agencies, distinguishing between domestic and foreign targets in the internet age is not an easy problem to solve.

Especially considering they're damned when they go too far (e.g. Prism) and damned when they don't (9/11).