FILE - In this July 2, 2013, file photo President Barack Obama, right, and former president George W. Bush shake hands with family members of victims of the U.S. Embassy bombing in Tanz

 

              FILE - In this July 2, 2013, file photo President Barack Obama, right, and former president George W. Bush shake hands with family members of victims of the U.S. Embassy bombing in Tanz
FILE - In this July 2, 2013, file photo President Barack Obama, right, and former president George W. Bush shake hands with family members of victims of the U.S. Embassy bombing in Tanzania during a wreath laying ceremony at the U.S. Embassy in Dar es Salaam. In the first 200 years of the republic, just three ex-presidents survived more than two decades after leaving office: John Adams, Martin Van Buren and Herbert Hoover. The odds have improved since then: Jimmy Carter, the longest-serving ex-president, has blown past 32 years out of office and shows no signs of stopping at age 88. George H.W. Bush, 89, passed the two-decade mark this year. The two most recent former presidents, Bill Clinton and George W. Bush, both are going strong. (AP Photo/Evan Vucci, File)