The NSA is a foreign signals intelligence service principally, though not exclusively, supporting the military. I don't really see any argument that the existence of the NSA -- however much the case may be made of particular activities of the NSA violating various provisions of the Constitution -- is any less within the purview of Art. I Sec. 8 enumerated powers (particularly, the power to "raise and support armies") than any other non-uniformed part of the military support structure in the US government.