The Nikki Haley Civil War flap reminds us about three things.
First, many Democrats truly believe (or at least are happy to claim to believe) there’s a big racist contingency among Republicans that I simply have not seen, at least in several decades.
Second, progressive Democrats will happily take the conflicting position and insist that the Civil War actually had nothing to do with slavery when their purpose is to malign the United States as no different than it was in the antebellum period. In those contexts, they’ll claim the Civil War was exclusively about the economic or political interests of white people, with slavery as little more than an excuse, and I can’t remember ever seeing their fellow Democrats express disapproval.
Third, partisan activists in the mainstream media can still get their constituencies riled up to make minor bumbles from Republicans, which are understandably more common in a live setting, seem like major revelations about their true beliefs.