White House: NSA chief has had 'extraordinary tenure'

"General Alexander has served an extraordinary tenure and capably led these agencies through critical periods of growth and transition," she said. "The president looks forward to continuing to work with General Alexander until his term is complete and thanks him, and the men and women of the NSA, for their patriotism and dedication as they work every day to keep us safe."

In addition to being the head of the surveillance agency, Alexander also leads U.S. Cyber Command, a team of military hackers that trains for offensive cyberattacks and protects U.S. computer systems. 

Since the Snowden leaks put the NSA in the spotlight, Alexander has launched a public relations campaign to try to rally support for the controversial surveillance programs. In public speeches and in open and classified congressional hearings, Alexander has argued that the programs provide critical information to thwart terrorist attacks. He also claims officials are careful to protect privacy rights.

But several lawmakers, including Senate Judiciary Committee Chairman Patrick LeahyPatrick Joseph LeahyGraham calls for Senate Judiciary hearing on McCabe firing McCabe firing roils Washington Judiciary Dem calls for hearing on Trump's FBI attacks MORE (D-Vt.), are working on legislation to rein in the NSA's power and toughen oversight.  

Although Alexander has been aggressive in defending the programs, he has not faced the same level of criticism as James Clapper, the director of national intelligence. Sen. Rand PaulRandal (Rand) Howard PaulTrump formally sends Pompeo nomination to Senate Spending bill delay raises risk of partial government shutdown support Overnight Defense: Senate sides with Trump on military role in Yemen | Dem vets push for new war authorization on Iraq anniversary | General says time isn't 'right' for space corps MORE (R-Ky.) and Rep. James Sensenbrenner (R-Wis.) have called for Clapper to resign over misleading comments he gave during a Senate Intelligence Committee earlier this year.