You can't win in South Carolina by splitting votes because of plurality voting laws here.
A candidate must get 50% + 1 vote to win the election. Any less, and there will be a run-off. So if you're saying two similar candidates would split the vote and let Graham win, wouldn't matter because you're also saying over 50% of South Carolinians voted Graham. So he would have hypothetically won anyways if there werent two splitting the same vote base.
Perfect example of this is Ted Cruz in 2012. He lost to the Lt Gov (Brewer) in the Senate race by more than 10 points. He and others had also split the vote, and Brewer had garnered about 45% of the vote. But because of plurality laws, Cruz and Brewer had a runoff election. The split base rallied behind Cruz, and Cruz walloped Brewer by more than 10 points.