US President Barack Obama, First Lady Michelle Obama and daughters Malia and Sasha step off the Marine One helicopter to board Air Force One at Cape Cod Air Force Station in Massachusetts on August 21, 2016 as they depart for Washington after a two-week holiday at nearby Martha's Vineyard. / AFP PHOTO / NICHOLAS KAMMNICHOLAS KAMM/AFP/Getty Images

US President Barack Obama, First Lady Michelle Obama, daughters Malia and Sasha board Marine One at Martha's Vineyard airport in Edgartown, Massachusetts, on August 21, 2016 as they depart for Washington after a two-week holiday on the island. / AFP PHOTO / NICHOLAS KAMMNICHOLAS KAMM/AFP/Getty Images

(FILES) This file photo taken on March 4, 2016 shows a view of the Old Post Office building as it is converted to the Trump International Hotel in Washington, DC. Companies belonging to Donald Trump have at least $650 million in debt, more than twice the amount shown in public filings made by his presidential campaign, the New York Times reported August 20, 2016. The paper employed a property information firm to search publicly available data on more than 30 US properties connected to the Republican candidate, including offices and golf courses. / AFP PHOTO / Brendan SmialowskiBRENDAN SMIALOWSKI/AFP/Getty Images

ATLANTA, GA - AUGUST 19: Atlanta Braves President John Schuerholz acknowledges the crowd as he rides around the field in honor of his induction into the Atlanta Braves Hall of Fame before the game between the Atlanta Braves and the Washington Nationals at Turner Field on August 19, 2016 in Atlanta, Georgia. (Photo by Mike Zarrilli/Getty Images)

The headquarters of the Democratic National Committee is seen in Washington, U.S. June 14, 2016. REUTERS/Gary Cameron

FILE - AUGUST 19, 2016: It was reported that Paul Manafort issued his resignation to Republican Presidential candidate Donald Trump August 19, 2016. WASHINGTON, DC - APRIL 27: Paul Manafort, advisor to Republican presidential candidate Donald Trump's campaign, checks the teleprompters before Trump's speech at the Mayflower Hotel April 27, 2016 in Washington, DC. A real estate billionaire and reality television star, Trump beat his GOP challengers by double digits in Tuesday's presidential primaries in Pennsylvania, Maryland, Deleware, Rhode Island and Connecticut. "I consider myself the presumptive nominee, absolutely," Trump told supporters at the Trump Tower following yesterday's wins. (Photo by Chip Somodevilla/Getty Images)

(FILES) This file photo taken on January 6, 2016 shows State Department Spokesman John Kirby speaking during the daily briefing at the State Department in Washington, DC. The United States acknowledged that it waited for Iran to release American prisoners before delivering $400 million in cash that it owed the country, but again insisted the payment was not ransom.Republicans including Donald Trump pounced on the August 18, 2016 admission as proof that President Barack Obama's government had misled the American people "With concerns that Iran may renege on the prisoner release... we of course sought to retain maximum leverage until after American citizens were released," State Department spokesman John Kirby told reporters."That was our top priority," he said. / AFP PHOTO / MANDEL NGANMANDEL NGAN/AFP/Getty Images

Republican U.S. presidential nominee Donald Trump holds a campaign rally at the ​Ziegler Building at the Washington County Fair Park & Conference Center in West Bend, Wisconsin August 16, 2016. REUTERS/Eric Thayer/File Photo