The astonishing political events of the last four weeks make plain, once again, how much of America’s history depends on what voters have come to accept as the choice of one person: each presidential nominee’s choice of a vice presidential candidate. Even as the nomination process was expanded, half a century ago, to include millions of primary voters, the choice of the vice presidential nominee has devolved from smoke-filled rooms of bosses who represented large constituencies to the choice of a single person.

Consider the 47-year-old Barack Obama’s selection of 65-year-old Joe Biden in 2008. For 2016, Obama shoved Biden aside in favor of the rival he bested in the February 2008 primaries, Hillary Clinton. The Biden family and many others think their man would have beaten Donald Trump and would be in the twilight of an eight-year presidency now.