OTL Trey Gowdy contemplated primarying Lindsey Graham in 2014, but Boehner made Gowdy Chair of the House Benghazi Committee with the intention of blocking him from going after Graham.
What if Gowdy had primaried Graham and been elected Senator?
Gowdy has a good working relationship with Tim Scott (they even co-wrote a book together), is less Hawkish than Graham (not saying much tbh), more concerned about 4th amendment issues, and more economically-minded.
Assuming Trump is still elected, he seems more likely to push back against Trump given how he'd criticize him from time to time.
Meanwhile, somebody else would be heading up the Benghazi Committee. Susan Brooks was the number two Republican in the committee and as US Attorney, so I could see her being the one to do it. Maybe this would mean she'd be a statewide candidate in 2016 (Governor) or 2018 (Senator).