FILE - In this April 25, 2013, file photo, former presidents, from left, George W. Bush, Bill Clinton, George H.W. Bush, and Jimmy Carter gather for a ceremony in Dallas, Texas. In the first 200 years... more 
FILE - In this April 25, 2013, file photo, former presidents, from left, George W. Bush, Bill Clinton, George H.W. Bush, and Jimmy Carter gather for a ceremony in Dallas, Texas. 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/Charles Dharapak, File) less 
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Associated Press | Photo By Charles Dharapak, File
Mon, Jul 22, 2013 1:13 PM EDT