US President Barack Obama crosses The South Lawn before boarding Marine One at The White House August 26, 2016 in Washington D.C. President Obama will visit wounded service members at Walter Reed National Military Medical Center in Bethesda, Maryland. / AFP PHOTO / ZACH GIBSONZACH GIBSON/AFP/Getty Images

US President Barack Obama exits The Oval Office before boarding Marine One at The White House on August 26, 2016 in Washington D.C. President Obama will visit wounded service members at Walter Reed National Military Medical Center in Bethesda, Maryland. / AFP PHOTO / ZACH GIBSONZACH GIBSON/AFP/Getty Images

WASHINGTON, DC - AUGUST 26: U.S. President Barack Obama departs the White House on August 26, 2016 in Washington, DC. Obama was scheduled to visit the Walter Reed National Military Medical Center after leaving the White House. (Photo by Win McNamee/Getty Images)

WASHINGTON, DC - AUGUST 26: U.S. President Barack Obama waves while departing the White House on August 26, 2016 in Washington, DC. Obama was scheduled to visit the Walter Reed National Military Medical Center after leaving the White House. (Photo by Win McNamee/Getty Images)

WASHINGTON, DC - AUGUST 26: U.S. President Barack Obama departs the White House on August 26, 2016 in Washington, DC. Obama was scheduled to visit the Walter Reed National Military Medical Center after leaving the White House. (Photo by Win McNamee/Getty Images)

Former World Bank president Paul Wolfowitz leaves his house in the Washington suburb of Chevy Chase, Maryland, in this file photo dated May 17, 2007. REUTERS/Yuri Gripas

(FILES) This file photo taken on August 4, 2016 shows US President Barack Obama as he speaks at a press conference at the Pentagon in Washington, DC. President Barack Obama will travel to his native Hawaii August 31, 2016 to establish the world's largest marine reserve and burnish his environmental legacy.The outgoing president will announce a massive expansion of the Papahanaumokuakea Marine National Monument across a swath of the Pacific. The protected area, which is already bigger than Greece or North Korea, will almost quadruple in size to 582,578 square miles (1.5 million square kilometers) the White House said. / AFP PHOTO / Brendan SmialowskiBRENDAN SMIALOWSKI/AFP/Getty Images

U.S. President Barack Obama speaks from the Rose Garden of the White House to announce his three nominees to fill vacancies on the United States Court of Appeals for the District of Columbia in Washington June 4, 2013. The nominees will be attorney Patricia Ann Millett (R), Georgetown law professor Cornelia Pillard (behind Obama) and U.S. District Court Judge Robert Leon Wilkins (L). REUTERS/Kevin Lamarque/File Photo