In 1964, Goldwater picked as his running mate William E. Miller. Miller was a unknown congressman from Upstate New York who Goldwater picked because he was a loyal Republican and Goldwater said he bugged LBJ (though I don't know if LBJ even knew who the Hell Miller was). Miller certainly didn't help Goldwater at all, though Goldwater was always going to lose, and Goldwater went on to lose by a landslide.
Who else could have been Goldwater's running mate in 1964?