FILE - In this April 25, 2013, file photo President Barack Obama, from left, and four former presidents, George W. Bush, Bill Clinton, George H.W. Bush and Jimmy Carter appear together at a dedication... more 
FILE - In this April 25, 2013, file photo President Barack Obama, from left, and four former presidents, George W. Bush, Bill Clinton, George H.W. Bush and Jimmy Carter appear together at a dedication 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/David J. Phillip, File) less 
1 / 26
Associated Press | Photo By David J. Phillip, File
Mon, Jul 22, 2013 2:12 PM EDT