U.S. President Barack Obama pauses while hosting a conversation on community policing and criminal justice at the White House in Washington July 13, 2016. REUTERS/Kevin Lamarque

U.S. Airways President Scott Kirby speaks at the Reuters Aerospace and Defense Summit in Washington December 5, 2006. REUTERS/Yuri Gripas

Washington, USA; Patrick Hickey, ANOC senior vice president and president of the European Olympic Committees, poses on the blue carpet prior to the 2015 ANOC Awards at DAR Constitution Hall. Mandatory Credit: Geoff Burke-USA TODAY Sports/File Photo

U.S. President Barack Obama waves as he walks out from the White House before his departure to view flood damaged area in Baton Rouge, in Washington, U.S., August 23, 2016. REUTERS/Yuri Gripas

Former U.S. Secretaries of State meet with President Barack Obama to discuss the Trans-Pacific Partnership (TPP) at the White House in Washington, November 13, 2015. REUTERS/Kevin Lamarque

(FILES) This file photo taken on February 24, 2016 shows US Senator John McCain, Republican of Arizona, during a Senate Foreign Relations committee hearing about modern slavery on Capitol Hill in Washington, DC. John McCain faces perhaps the toughest re-election bid of his long US Senate career August 29, 2016 when he competes in an Arizona Republican primary overshadowed by party presidential nominee Donald Trump. The former US Navy pilot, who turned 80 on Monday, is a leading member of the Republican establishment in Washington and the party's 2008 presidential nominee. But his Republican challenger Kelli Ward has attacked McCain as perhaps too old to live out his sixth term should he win. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

(FILES) This file photo taken on August 26, 2016 shows US President Barack Obama arrives at The White House in Washington DC. US President Barack Obama will meet his Turkish counterpart Recep Tayyip Erdogan on Sunday in China on the sidelines of the Group of 20 summit, with Syria high on the agenda, top aide Ben Rhodes announced August 29. / AFP PHOTO / ZACH GIBSONZACH GIBSON/AFP/Getty Images

Former U.S. Secretaries of State meet with President Barack Obama to discuss the Trans-Pacific Partnership (TPP) at the White House in Washington, November 13, 2015. REUTERS/Kevin Lamarque