MYRTLE BEACH, S.C. — It’s conventional wisdom in Republican circles here in South Carolina that if Mitt Romney wins the state’s primary this Saturday — having already won in Iowa and New Hampshire — he’ll be the GOP presidential nominee.

“If for some reason he’s not derailed here and Mitt Romney wins South Carolina — no one’s ever won all three — I think it should be over,” Sen. Lindsey Graham said Sunday. “That would be quite a testament to his ability as a candidate and a campaigner.”