In neither case were voters moved by the “heartbeat away” concern. McKinley and Eisenhower both won easily.

Should voters be alarmed by a relatively young or inexperienced vice-presidential candidate? No. Since 1900, five vice presidents have succeeded to the presidency during their term in office: Teddy Roosevelt in 1901, Calvin Coolidge in 1923, Harry Truman in 1945, Lyndon Johnson in 1963, and Gerald Ford in 1974. Teddy Roosevelt took over at age 42, becoming our youngest president, and he’s generally thought to have proved up to the job. Truman was V.P. for less than three months and had been kept in the dark by Franklin Roosevelt about such matters as the atom bomb  and he’s generally thought to have risen to the occasion. Character, judgment and the ability to learn seem to matter more to success as president than the number of years one’s been in Washington.

Did McCain think Palin his very best possible successor? Perhaps not. Did Barack Obama think Biden the absolute cream of the Democratic crop? Perhaps not. They undoubtedly thought highly enough of their running mates to have confidence in their ability to take over their administration in case of incapacity or death. I think most voters will accept that basic judgment.

But  shocking to say!  both Obama and McCain also took political considerations into account in making their selections.

One thing McCain undoubtedly had in mind was Obama’s failure to pick Hillary Clinton. As The Times’s Patrick Healy reported Friday, “If the election remains close, the next president could very well be picked by what Chris Lehane, a Democratic strategist, calls ‘Wal-Mart Moms’  white working women with children living in the exurbs and in rural parts of battleground states. ...”

McCain didn’t just pick a politician who could appeal to Wal-Mart Moms. He picked a Wal-Mart Mom. Indeed, he picked someone who, in 1999, as Wasilla mayor, presided over a wedding of two Wal-Mart associates at the local Wal-Mart. “It was so sweet,” said Palin, according to The Anchorage Daily News. “It was so Wasilla.”

A Wasilla Wal-Mart Mom a heartbeat away? I suspect most voters will say, No problem. And some  perhaps a decisive number  will say, It’s about time.