Air Force Gen. Paul J. Selva, the vice chairman of the Joint Chiefs of Staff, addresses the 672 graduates at the National Defense University, Fort Lesley J. McNair, Washington, D.C., June 8, 2017. He described the outgoing students as critical thinkers and challenged them to be relentless in their assessment of the world as it is and how they can work to shape the world and defend freedom and liberty. DoD photo.