The pattern is markedly different in the five states that hug the Atlantic coast from Virginia to Florida, which together hold82 of the South’s 160 electoral votes. A combination of a growing black population, urban expansion, oceanfront development and in-migration from other regions has opened up increasing opportunities for Democrats in those states.

“Georgia is an achievable target for Democrats in 2016,” said Atlanta Mayor Kasim Reed, a frequent Obama surrogate during the campaign. “What you’re going to see is the Democratic Party making a drive through the geography from Virginia to Florida.”

That will be easier said than done — particularly when the Democratic nominee is not Obama — but powerful forces in the region are clearly eroding GOP dominance. The trends pose difficulties for a Republican Party that has been shifting toward Dixie since the “Southern strategy” of the Nixon era, which sought to encourage white flight from the Democratic Party.

In every Southern state except Louisiana, the population of African Americans grew substantially faster than that of whites over the past decade. The growth is fueled by black retirees from the north and rising numbers of young, well-educated blacks in prosperous cities such as Atlanta, Norfolk, Charlotte and Charleston, S.C.