He rode the Ferris wheel and drank lemonade. He threw darts at balloons. He won a prize after a carnival barker wrongly guessed his weight at 264 pounds — four pounds too high.

For three hours, Mr. Greene, 33, did just about everything at the fair except attend to the task at hand. As South Carolina’s unlikely Democratic nominee for the Senate, he was supposed to introduce himself, shake hands and ask for votes. It was, after all, just days before the election, and he had scheduled so few outings.

Instead, he brushed by most fairgoers, making little eye contact and little attempt to engage them. He did tell a few of them, in passing, that Senator Jim DeMint, his Republican opponent, had caused the recession.