I think the three most important GOP senators in this might prove to be the three oldest, Inhofe, Shelby and Grasley. They are all in their late 80's and likely in their final terms so they don't have to worry about getting primaried by a MAGAt. With McConnell dropping the whip, they are free to vote however they see fit. If they join the five (Romney, Toomey, Sasse, Collins, Murkowski) who have already indicated that they are open the idea of voting to convict then I feel at that point McConnell and Blunt (both who may be eyeing retirement too) join them and then the floodgates are open.