1964
I'm reading an account of the 1964 presidential election, Lyndon Johnson / Hubert Humphrey v. Barry Goldwater / William Miller.
The night of the nomination of Barry Goldwater LBJ received a poll that he would win 70% / 30%. And then Goldwater, instead of nominating a moderate to balance the ticket chose Miller, another hard-core conservative. Johnson won with 62% of the popular vote, all 538 electoral college votes.
One of the sad outcomes of all that is that Johnson did not want to be vulnerable to a "soft on communism" charge, and escalated Vietnam.