Despite several attempts by civic groups and news organizations to schedule debates, the candidates have agreed to only one. They will take the stage together on Monday at the Citadel, where every one of the 500 seats has long been reserved.

The next day the candidates, including Eugene Platt of the Green Party, a former Army paratrooper, will appear together at a forum sponsored by a local chapter of the N.A.A.C.P.

In a race expected to have a low turnout, the black vote could mean a lot. About 22 percent of registered voters are black, and most of them vote Democratic in a country club Republican district that supported Mitt Romney in the 2012 presidential election by 18 percentage points.

Still, even with the two candidates side by side, it might be hard to parse the differences. Each accuses the other of not being supportive enough of Boeing, which is based in the Charleston area and is the largest private sector employer in the state.

Both give a nod to the importance of education and conservative government spending. Each has laid claim to being the best fiscal manager, with Ms. Colbert Busch referring to her experience as a business executive in the maritime industry and as a mother who had to start with nothing after a messy divorce left her to raise three children alone.