President Obama

US President Barack Obama waves as he disembarks from Air Force One at the Tan Son Nhat airport in Ho Chi Minh City on May 24, 2016. Obama told communist Vietnam that basic human rights would not jeopardise its stability, in an impassioned appeal for the one-party state to abandon authoritarianism. / AFP PHOTO / CHRISTOPHE ARCHAMBAULTCHRISTOPHE ARCHAMBAULT/AFP/Getty Images

Christophe Archambault/AFP Photo

US President Barack Obama waves as he disembarks from Air Force One at the Tan Son Nhat airport in Ho Chi Minh City today.

Photographers in the press pen as Prime Minster David Cameron welcomes US President Barack Obama to Downing Street

Lauren Hurley/PA

Photographers in the press pen as Prime Minster David Cameron welcomes US President Barack Obama to Downing Street

President Barack Obama returns a salute as he boards Air Force One before his departure from Andrews Air Force Base, Maryland. USA

Pablo Martinez Monsivais/AP

President Barack Obama returns a salute as he boards Air Force One before his departure from Andrews Air Force Base

U.S. President Barack Obama (C) reviews a marsh band during a welcome ceremony at the National Palace in Addis Ababa, Ethiopia July 27, 2015

Tiksa Negeri/Reuters

U.S. President Barack Obama (C) reviews a marsh band during a welcome ceremony at the National Palace in Addis Ababa, Ethiopia today.

Russia's President Vladimir Putin, gestures as he walks past U.S. President Barack Obama, as he takes his place at a group photo outside of the Konstantin Palace in St. Petersburg, Russia .

Ivan Sekretarev/AP

Russia’s President Vladimir Putin gets a laugh as he takes his place at a group photo of G20 leaders outside the Konstantin Palace in St Petersburg, Russia.

President Barack Obama shakes hands and meets Tanzanians during an official arrival ceremony hosted by Tanzania President Jakaya Kikwete and First lady Salma Kikwete in Dar Es Salaam

Gary Cameron/Reuters

US President Barack Obama shakes hands with Tanzanians during an official arrival ceremony hosted by Tanzania President Jakaya Kikwete and First lady Salma Kikwete in Dar Es Salaam.

A jetliner flies over flags flying at half-staff at the Washington Monument in Washington, Tuesday, April 16, 2013

David Ake/AP

A jetliner flies over flags flying at half-staff at the Washington Monument in Washington, Tuesday, April 16, 2013, after President Obama ordered flags to be lowered on federal building to honor the loss of life from the explosions at the Boston Marathon.