President Obama

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.