President Barack Obama and Gen. Martin Dempsey, Chairman of the Joint Chiefs of Staff, attend the September 11th Observance Ceremony at the Pentagon Memorial in Arlington, Va., Sept. 11, 2014.

President Barack Obama and Gen. Martin Dempsey, Chairman of the Joint Chiefs of Staff, attend the September 11th Observance Ceremony at the Pentagon Memorial in Arlington, Va., Sept. 11, 2014.