a) Goldwater was no Donald Trump. He lacked the charm, energy, and crusading bullet-points of the Trump juggernaut
b) Back in 1964 there was a Leftist monopoly on ALL TV Media, and most print media; Goldwater was up against JFK's Legacy, Johnson's Propaganda Machine, and the Establishment GOP -- all lined up against Goldwater
c) Once a political game-plan is sussed-out, the antidote is easy for Team Trump.
In Hitlery's case, what's clearly evident to many is that she and her sickly campaign cannot match the Trump campaign's energy, optimism, AND its war mode and momentum.
Even I could think up a dozen very effective ads against Clinton. And $500mil worth of those will change some votes.