"There is the world of difference between republican party of pre civil rights days and post civil rights days."- So "Civil Rights" had a detrimental impact.
Indeed it did JLM, on the Republican party. All the segregationists in the south were mad at the Democratic Party for supporting Civil Rights legislation and other civil rights initiatives (voting rights act etc.), so they drifted to Republican party en masse.
Before the 70s, the South used to vote overwhelmingly Democratic. Indeed, there was a saying in Texas, that there will never be enough Republicans in Texas to hold a primary. These days, it is exactly the opposite, there are not enough Democrats in Texas to hold a primary. The governor, both the senators and majority of House members from Texas are Republican.
These days Republican party is the party of God, the party of intolerance. It didn’t use to be that way.