The chairman of the federal government board overseeing surveillance and civil liberties — the agency that questioned the legal validity of National Security Agency’s warrantless spying — resigned Tuesday from his post two years before the end of his term.

David Medine, the departing head of the Privacy and Civil Liberties Oversight Board, led the agency in its critical 2014 report on the NSA’s mass surveillance of Americans’ telephone calls. Medine said in a statement that he was leaving the board to take a private position advising on data privacy for an unnamed development organization.

Medine led the board during its review of secret surveillance operations commissioned by President Barack Obama. The board found that the NSA’s phone surveillance program, which targeted telephone calls made by millions of Americans, had a flimsy legal foundation and did not lead to significant counterterrorism investigations by federal law enforcement agencies. Obama ordered the review in the wake of revelations about the long-secret NSA surveillance made by former Edward Snowden, a former contractor for the intelligence agency.

In a statement, Obama praised Medine for “skilled stewardship” during the administration’s reassessment of its surveillance programs. “Under David’s leadership, the PCLOB’s thoughtful analysis and considered input has consistently informed my decision-making.”

Obama did not always agree with the recommendations that Medine and the board offered. The administration rejected the board’s critique about the surveillance program’s faulty legal basis. “The administration believes that the program is lawful,” said then-administration spokesman Jay Carney soon after the report’s release in January 2014.

The board’s legal critique was later echoed by a ruling against the government’s surveillance program by a federal district judge in Washington. But the administration ultimately made those arguments moot when it halted the massive phone surveillance program last November and reorganized a more limited version of the operations under a new law, the USA Freedom Act.

The board, which can examine classified material but has only advisory authority, has been in existence since 2007 under congressional mandate. It was long hampered by budgetary and structural problems until Medine’s appointment in 2013. In recent years, supporters in Congress have pressed to expand the board’s authority to include subpoena power, but opposition by other legislators left the organization in its current advisory role.

In his statement, Medine said that support from Obama and Congress, “the board has been able to carry out its timely mission of conducting oversight and providing advice to ensure that federal counterterrorism efforts properly balance national security with privacy and civil liberties.”

(AP)