On Election Day, Jim DeMint usually goes to an afternoon movie with his wife. “I’ve been in a few squeakers and it helps to get my mind off things,” says the Republican senator from South Carolina. “I turn off my cell phone and try to forget.”

This year was different. “There was too much going on,” he says. “I stayed up until about two in the morning, watching the returns come in.” DeMint wasn’t talking about his own race, which was no squeaker this time: He won a second term with 62 percent of the vote. Instead, he was referring to …