The RGA has recently began to go after Edwards in full force. The plan seemed to be to just attack Vitter's Republican opponents since he would have a more difficult time beating one of them in a run-off. With the GOP fighting among itself here, the Democrat enjoys a united party and (up until this point) very little negative anything. Edwards is likely to fall some with the RGA onslaught currently underway, and a run-off with tighten somewhat once all GOP energy is focused on Edwards. That being said, Edwards holds a statistically significant lead now in multiple polls. He may be too well situated and Vitter may be just too damaged for this race to end up going the Republican's way this fall. This (along with Kentucky) will be a fascinating race to continue to watch develop.
As a side note, the RGA's new-found interest in this race might signify that they are more concerned in saving Vitter than they are with saving Bevin in Kentucky. That might be a wise move on their part. Though, that could backfire if Edwards holds on and Democrats run the table in Kentucky.