FILES- Picture taken on September 21, 2009, shows US President Barack Obama (L) joking with David Letterman during a taping of the Late Show with David Letterman in New York. Letterman celebrates his 65 birthday on April 12, 2012. AFP PHOTO/JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
FILES- Picture taken on September 21, 2009, shows US President Barack Obama (L) joking with David Letterman during a taping of the Late Show with David Letterman in New York. Letterman celebrates his 65 birthday on April 12, 2012. AFP PHOTO/JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)

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