The NSA as it exists is essentially the government telling you the 4th Amendment is just for show. The NSA takes broad measures under the blanket of "national security" and through its 5 Eyes partners, can pretty much do as it pleases, either with US Citizens, or foreign citizens.

EDIT: Former NSA directors have deliberately lied under oath to Congress about their activities and actions...with no penalty or rebuke. The NSA are above the law and constitution.