Alec MacGillis offers another reason for Romney's failure to connect with Southerners: 

In the region that prizes military service more than any other, Bush’s aviation heroics, Dole’s paralyzed right arm and McCain’s years in North Vietnamese captivity lent them fundamental credibility and a connection with voters, particularly fellow veterans. McCain might’ve disagreed about voters in South Carolina about immigration or climate change, but he could crack one of his Marine jokes, or go on one of his solemn Country First turns, and have the crowd eating out of his hand. With Dole and Bush, the appeal was less explicit, but it was still there; everyone knew where they’d been. 

Romney has nothing to draw on here.

Quite the opposite—when he was asked in 2007 why none of his five sons had served in the military, he answered, to widespread derision, "One of the ways my sons are showing support for our nation is helping to get me elected." Making matters trickier for Romney, this factor is in fact linked with his religion: He avoided being drafted during the Vietnam War by claiming an exemption for his 30-month missionary duty in France.