They swore an oath to protect the Constitution.

https://www.law.cornell.edu/uscode/text/5/3331

They even reaffirmed it late last year.

(sorry for the google cache link; www.nsa.gov (AkamaiGHost?) is currently returning 503 Service Unavailable)

https://webcache.googleusercontent.com/search?q=cache:-yz7S-...