The GOP was a mass political party then, with liberals, centrists, and conservatives — the latter had been defeated and marginalized since 1932. The 1952 nomination fight loss of Sen. Robert Taft, "Mr. Republican," to the centrist Dwight Eisenhower had been especially embittering to the right.
The party was controlled by the generally liberal Eastern establishment. But in the 1964 national convention, its leading candidate, New York Gov. Nelson Rockefeller, was smashed by the Goldwater machine at the Cow Palace in San Francisco.
The department store heir embraced the reactionary right's agenda to roll back the New Deal and confront the Soviet Union much more aggressively. Goldwater opposed federal civil rights legislation, a stance he later came to regret but it attracted Southern whites. He didn't want to run against the ghost of the recently martyred John F. Kennedy (who, when alive, had worried about a Goldwater challenge). But he felt it was his duty to the party and his conservative principles.
Of course Goldwater went down in one of the worst drubbings in the history of presidential elections. He carried only six states: Arizona (despite Eugene C. Pulliam endorsing LBJ) but more significantly for the future four states in the Deep South and South Carolina. Of equal significance was the visible support of actor Ronald Reagan, especially his famous "Time for Choosing" speech on the eve of the election. It made Reagan a political star and Goldwater's heir presumptive.
We can wonder what Barry and Dutch would think of Donald Trump, Ted Cruz, et al, and I have speculated that both would now be seen as "too liberal" to win a GOP school-board election. But the fact is that they built today's white, extreme-right Republican Party and everything it has brought to our national politics, life, and future. Much of Reagan's 1964 speech echoes eerily into our present.
Which brings us to Sen. Bernie Sanders.