Sen. John Kerry got to be the leading candidate for the Democratic presidential nomination through a series of embarrassing verbal gaffes by his major opponent, Howard Dean. But Kerry has made his share of mistakes in the past. One that may come back to haunt him – particularly as he begins considering vice presidential candidates – is the one he told about Dan Quayle on Nov. 16, 1988. "Somebody told me the other day that the Secret Service has orders that if George Bush is shot, they're to shoot Quayle," he said. "There isn't any press here, is there?" After...