He was very anti Trump and then later pro Trump. Though it's not clear it's a result of coercion or anything other than Graham capitulating to work to get stuff done
He's a republican. The approach he used - if you can't beat them then join them. Not sure if T has any dirt on him.
Along the lines - Chris Christie was also very anti T before T got the nomination.
He switch almost immediately after McCain died. Almost as if McCain had some kind of hold over him.