July 13, 1972: Democratic presidential nominee George McGovern selects Thomas Eagleton, a senator from Missouri, as his running mate. 

August 1, 1972: Eagleton withdraws from the ticket.   

According to the St. Louis Post-Dispatch, Eagleton had been hospitalized for mental health issues, including depression, three times between 1960 and 1966, and had undergone electro-convulsive therapy – also known as electroshock therapy – for "exhaustion and fatigue." Eagleton was also taking Thorazine, a powerful anti-psychotic drug, information that had not been  disclosed to McGovern prior to his selection of Eagleton.

In a Time magazine poll conducted that summer,  76.7% of respondents said that Eagleton's mental health record would not influence their votes.  But there clearly was concern that given the pressures that come with being vice president and, potentially, the president, Eagleton was at risk for a recurrence of mental health problems. So, despite initially expressing “1000 percent” confidence in his running mate, McGovern soon decided to drop Eagleton from the ticket.

So what role does the health of a president play in his electability? 

Historical precedent certainly exists. President Franklin Roosevelt, fearing that his political life may be in jeopardy if his disability became public, hid the fact that he was confined to a wheelchair due to the effects of polio.  FDR also was quite ill during the 1944 presidential campaign, and died of a stroke just a few months after beginning his fourth term.

"President Roosevelt had real concerns that the public might not think that he was up for the job of being president," said Dr. John Kenneth White, professor of politics at the Catholic University of America and an expert on the U.S. presidency. 

"There has always been concern about the president and his health," White added, citing FDR, John F. Kennedy and Dick Cheney as others in high office who concealed their health status.  "Only in the last 30 or 40 years have we had presidents release health information to the public as a matter of routine."  Just last week, Republican presidential candidate Mitt Romney and his running mate, Rep. Paul Ryan, released their health records.

However, as White noted, Roosevelt and Kennedy held office during a very different era.  "In the cable and YouTube age, a president wouldn't be able to hide anything,” he said. “There is a sense of wanting presidents to be the model of physical fitness."  White provided examples from the more recent past, including a Parade magazine featuring President Reagan lifting weights, Ted Kennedy losing a significant amount of weight before a presumed run at the presidency in 1980 and George W. Bush's penchant for bicycling.  "Especially in the television age, the president must present an image of physical fitness – we certainly have two very healthy candidates in this cycle."