Once people have served as the president of the United States, they are faced with the question of what to do with the rest of their lives.

Some live for several years after their term ends but others do not. Sadly, eight presidents – four who were murdered and four who died of natural causes – never had the chance to experience life as an ex-president at all.

Fortunately, however, people – including former presidents – are living longer than used to be the case. Consequently, many former presidents have several years of life left in them once they cease being president.

When Herbert Hoover di...