I'm not sure. I don't think most Republicans are racist, although most racists now do find a home in the Republican Party. It's not a coincidence that the Civil Rights Act was passed and Southern whites began switching en masse to the Republican Party, most notably Strom Thurmond in 1964. Although it has taken a few decades, the realignment of Southern whites to the Republican Party appears complete. With perhaps the exception of a favourite son in 1976, the party that has dominated the Deep South has been the home of racists.
The South was trending Republican from 1948 onwards. Obviously, the CRA of
1964 is reponsible for starting it. It augmented the trend, sure. But it was a combination of issues that flipped rural, white Southerners and race was one of many, and the CRA actually damaged the GOP in the southern states they had been previously gaining ground in VA, TN and FL. Of course you didn't distinguish, you just said Southern whites, which were trending GOP for over a decade before the CRA.
Now race did play a roll, along with generational change. With fewer Civil War generation members around, and the move towards Civil Rights by the Dems in 1948, there was little desire on the part of middle class professionals, small businessmen and white collar workers to continue voting differently than similar demographics elsewhere. So instead, they started voting for the Party of business and money.