Thanks for digging up the quote. I thought you were saying that Graham told Republicans this. Which would surprise me. Trump doesn't have to care about GOP senators but just ignoring them might not work so great either, because he's asking a lot of them, including signing on to a coverup without knowing exactly what they're covering up. Many disagree with him about Russia and Saudi Arabia, and not just for the sake of disagreeing - they seem to be actually concerned. They're losing face, IMO. Sooner or later something's got to give.
A third of the Senate is in play in the 2020 presidential race. So far they've gone all in with Trump. If that changes, the power dynamics will shift dramatically. It might not even take that much. In my state a GOP senator who rolls over for Trump at this point would (will) be vulnerable to both primary challengers and Democratic candidates.