Do vice-presidential picks matter?

SHORTLY AFTERLBJ announcing his run for the Democratic nomination in 1960, John F. Kennedy said: “I don’t recall a single case where a vice-presidential candidate contributed an electoral vote.” Still, the north-easterner picked Lyndon Johnson as his running-mate, hoping that the senator from Texas would help him in southern states. Johnson tore across the South in a train nicknamed the Express, arriving at rallies in a ten-gallon hat to the strains of “The Yellow Rose of Texas”. After he won, Kennedy admitted that “we couldn’t have carried the South without Johnson”. That Johnson “delivered the South” is now received wisdom. But how much difference do vice-presidential picks actually make in elections?