Admiral William McRaven, who supervised the 2014 Special Forces raid in Pakistan that killed Al-Qaeda kingpin Osama Bin Laden, resigned last month from the Defense Innovation Board, said Pentagon spokeswoman Lt. Col. Michelle Baldanza.

The resignation was effective on August 20, four days after McRaven published a scathing open letter to Trump in the Washington Post, blasting the president for punishing another critic, former CIA director John Brennan, by ordering Brennan's security clearance revoked.

Calling Brennan "one of the finest public servants I have ever known," McRaven wrote that "it would be an honor" to have his own security clearance revoked as well.

"Through your actions, you have embarrassed us in the eyes of our children, humiliated us on the world stage and, worst of all, divided us as a nation," McRaven said.

"If you think for a moment that your McCarthy-era tactics will suppress the voices of criticism, you are sadly mistaken," he said.

The letter resonated deeply, as few serving and former military officers had joined in the strong open criticism of Trump from the intelligence community and bureaucracy.

The Defense Innovation Board brings together top private sector technologists and scientists to advise the Pentagon and the Secretary of Defense.