ARLINGTON, VA - MAY 19: Chairman of the Joint Chiefs of Staff Marine Gen. Joseph F. Dunford Jr (R), U.S. Secretary of Defense Jim Mattis (C) and Special Presidential Envoy for the Global Coalition to Counter ISIS Brett McGurk (L) answer questions during a Pentagon briefing May 19, 2017 in Arlington, Virginia. Mattis, Dunford, and McGurk briefed members of the press on the status of U.S. President Donald Trump's campaign to defeat ISIS. (Photo by Win McNamee/Getty Images)