I think Paul Krugman is pretty wrong here:
And if you look at the political successes of the G.O.P. since it was taken over by movement conservatives, they had very little to do with public opposition to taxes, moral values, perceived strength on national security, or any of the other explanations usually offered. To an almost embarrassing extent, they all come down to just five words: southern whites starting voting Republican.
It's true that the recent political success of the GOP has an enormous amount to do with the party's success in the white south, but I think the evidence strongly suggests that conservative politicians get the votes of white southerners precisely because white southerners like conservative positions on taxes, moral values, and national security. Southern Democratic politicians of the Jim Crow era, after all, mostly took conservative stances on all of these issues. The weird thing about Jim Crow politics is that white southerners with conservative views on taxes, moral values, and national security would vote for Democratic presidential candidates who didn't share their views. They did that as part of a strategy for maintaining white supremacy in the South.
And for a long time the strategy worked. Democratic politicians like Woodrow Wilson and Franklin Roosevelt loyally upheld white supremacy. The dam began to crack with Harry Truman, and then under Lyndon Johnson the national party decisively broke with this corrupt bargain. With that done, white southerners just took their conservative views on taxes and national security into the Republican Party where such views belonged. Racism is a key part of the story, but it plays a much bigger role in explaining why Adlai Stevenson and John Kennedy won South Carolina than in explaining why Ronald Reagan and George W. Bush won there.