Under Franklin Roosevelt, the Democratic Party assembled a political coalition so vast and diffuse that it included the "solid south" voting bloc of white supremacists, but also included most African-American voters, who were attracted to the New Deal's economic program and who were beginning to be incorporated into some Northern political machines. This, in turn, helped spur the growth of a civil rights bloc inside the Democratic Party that saw its first meaningful stirrings during Harry Truman's administration. When Dwight Eisenhower came along to try to rebuild the Republican coalition, the GOP both pursued a strategy of trying to take advantage of Southern disgruntlement to win outer south states, and a strategy of trying to win black voters back over to the GOP. This latter strategy had some success in 1956 (driven in party by Ike's endorsement by Adam Clayton Powell, Jr.) but by the 1960 Kennedy-Nixon race those gains had all been re-erased. David Nichols recounts the post-election assessment discussion between Eisenhower, Richard Nixon, RNC chair Thruston Morton, and a few other White House aides (A Matter of Justice, page 262):
Ike turned the discussion to civil rights. He observed that Attorney General Rogers was "somewhat to the left" of himself on civil rights. Nixon groused that a statement during the campaign by his vice-presidential running mate, Henry Cabot Lodge, Jr., about possibly putting a Negro in the cabinet "just killed us in the South." Eisenhower bitterly complained: "We have made civil rights a main part of our effort these past eight years but have lost Negro support instead of increasing it." Negroes, the president said, "just do not give a damn." Nixon remarked that black loyalty to the Democrats was "a bought vote, and it isn't bought by civil rights." Morton agreed with the vice president and said, "the hell with them."
Eisenhower was tempted to agree with Morton, but he pulled the conversation back to a more civil tone. He would not say "the hell with them," although he could not comprehend why his efforts were not more appreciated. No one, he said, was "more sincere" than he was in "bettering opportunities" for African-Americans. He recalled reading about economic reprisals against Negroes in Tennesee and said that such reports still "infuriated him."
After a couple of years of dawdling, the Kennedy administration eventually got behind a strong civil rights program -- stronger than anything Ike had ever embraced -- and LBJ was able to get it passed through congress. With that done, the correct direction of the cynical calculation shifted decisively in favor of the Nixon/Morton "to hell with them" point of view and the rest, as they say, is history.