WASHINGTON, DC - APRIL 1: (AFP OUT) U.S. President Barack Obama, center, speaks during an opening plenary entitled 'National Actions to Enhance Nuclear Security' at the Nuclear Security Summit on April 1, 2016 in Washington, D.C., U.S. After a spate of terrorist attacks from Europe to Africa, Obama is rallying international support during the summit for an effort to keep Islamic State and similar groups from obtaining nuclear material and other weapons of mass destruction. (Photo by Andrew Harrer-Pool/Getty Images)
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