None of your examples are even within the last 100 years.
The lesson you
should take from history is that, in that time, the Democrats have moved forward on social issues, knowing they'd lose the support of some of their base, who were hard-core racists. And the Republicans, seeing an opportunity, deliberately slanted their stance and message to be significantly more appealing to those racists.
Nor am I exaggerating or using biased terminology. This is explicitly what the Republican
Southern Strategy was, when it was launched in the '60s.
Your entire premise doesn't work as an attack on Democrats, since the Democratic Party
recognized those failings, and sought to redress them. And the Republicans decided to adopt those failings, of their own free will, to win votes.