“You don’t rebuild Atlanta in a day,” Mr. Strider said.

After decades of decline from once-total control of the South, Democrats already had little left to lose before the election. Names of successful candidates past, like Carter, Nunn and Pryor, showed up in the loss column on Tuesday; Senator Kay Hagan of North Carolina came close but was defeated as well.

In perhaps the most emblematic victory, a Republican, Rick Allen, beat John Barrow of Georgia, the last white Democrat in the House from a Deep South state. His defeat was a testament to just how rare white Democrats have become in the region, a rarity that cuts across categories. In Georgia, according to exit polls by Edison Research, 80 percent of whites who did not graduate from college voted for David Perdue, the Republican Senate candidate. Among white college graduates, that number was not much lower, at 70 percent.

For Democrats and Republicans alike, there was a common culprit.

“It’s Obama,” Mike Beebe, a Democrat and the departing governor of Arkansas, said in his office at the State Capitol on Wednesday. “It wasn’t just Arkansas. It was all over the country. There’s only one common denominator.”