No one would classify Charleston as "ultra-red." The district is represented by disgraced adulterer Mark Sanford, but it was gerrymandered to include areas up the coast and conservative rural areas to insure it goes GOP. Charleston itself is very liberal for the South. They had a black Jewish police chief for several decades, and about three election cycles back an openly gay woman running as the Democrat lost the Congressional seat by 2%.

On edit: not meaning to buzzkill your post, but wanted to point out that Charleston is a liberal bastion in an otherwise very red state. The Bernie visit is generating a lot of local attention, and he will have a good size crowd there. I know there are a couple of buses making the trip from the U of SC for the event.