Graham will be debating his primary opponents.
http://www.thestate.com/2014/04/24/3407792/graham-agrees-to-sc-debate.htmlIt'll be on the Saturday before the primary and of course those opposed to Graham are treating the fact they've "forced" him to debate to be a victory. Maybe a moral victory, but that's all. Unless the polls are showing who will clearly be facing him in a possible runoff, his opponents are likely to spend a lot of their time attacking each other as they strive to make the runoff and I doubt Graham will agree to a second debate for the runoff if it is held, especially given that they already debated that month.
Anyway, it will be streamed on the internet for those of you who are interested.
There are plans for debates in some of the other races, but nothing has been finalized for those.