From a Washington Post report:
For congressional elections, southern Democrats’ plight appears even more hopeless. Because of the way districts are drawn and populations are concentrated, Democrats won just 28 percent of Southern House seats in 2012 despite receiving over 40 percent of the vote in those states. And these districts are not just a few percentage points away from becoming competitive due to demographic trends. Republicans hold a partisanship edge of at least 14 percent in 47 of 60 districts in the Deep South belt of the Carolinas, Georgia, Tennessee, Alabama, Mississippi and Louisiana. Barring national electoral reforms at the congressional level (such as FairVote’s recommendation of fair representation voting), there is no reason to think this situation will change after the next census in 2020.
If Democrats are counting on voters in South Carolina, Georgia, Mississippi and Texas to win them the White House and Congress in 2024, they might want to come up with a backup plan.