You are mistaken that the majority of white people shifted to the Republican party in response to the civil rights legislation. White Americans overwhelmingly voted IN the thousands of legislators and executives who passed the laws and appointed the judges that made the vast civil rights movement into law. The signal event was well after that. It was the Democrat's 1968 shift to "The New Left" which emphasized social justice over economic justice. Even MLK, the SCLC, etc., had long recognized that economic justice was the train that all other social justice, including civil rights had to hitch a ride on. The people we now deride as the Trump Base were exactly the people who elected all of the politicians responsible for the tsunami of civil rights and social justice legislation from FDR to RMN. What drove them out of the party was the New Left's idea of a "The Rainbow Coalition." It was a momentous shift of emphasis from economic justice, which all groups saw as being to their benefit, to social justice, which effectively alienated the white working class and LMC, who made up a large majority of the electorate. Go back and look for instance at the political platforms of 1968 and earlier. You literally cannot tell the Republicans and the Democrats apart without serious study. Either party needed the massive if boring base who cared primarily about economic justice: unions, minimum wage, child labor laws, support for home buying, etc. From the moment the Democrats shifted away, we haven't had a meaningful piece of social legislation, except title nine for women's athletics! Incredibly, Nixon, the supposedly arch right winger was actually to the LEFT of Bernie Sanders today. He was working on what he called "European style socialized medicine." when he resigned. Even though a Republican's Republican, he signed more progressive legislation than anyone other than LBJ and Roosevelt. That's how far we've fallen, largely because we Democrats refuse to look honestly at how we got here. You cannot demonize the Trump base as a basket of deplorables, and call them racists and sexists, and attribute all the evils of history to them without paying the electoral price.