Country music singer Brad Paisley performs during a troop rally with President Obama during an unannounced visit at Bagram Air Field on Sunday. Evan Vucci/AP hide caption

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San Antonio Mayor Julian Castro is a rising star in the Democratic Party. He spoke at the Democratic National Convention in Charlotte, N.C., in 2012. J. Scott Applewhite/AP hide caption

itoggle caption J. Scott Applewhite/AP

Reporter Harry McAlpin leaves the White House in 1944. McAlpin was the first black reporter to cover a presidential press conference. He'll be honored Saturday at the Correspondents' Dinner. George Skadding/Time & Life Pictures/Getty Image hide caption

itoggle caption George Skadding/Time & Life Pictures/Getty Image

President Obama was at Fort Bonifacio in Taguig, Philippines, on Tuesday, during the last leg of his four-nation tour through the Asia-Pacific region. Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP