Being president pretty much ends your power/influence. So if you don't get what you want accomplished, you're not getting it done. As a Senator, you get 6 years every time you win an election. With that, some people are more effective not being president.
Maybe don't use him as the archetypal example if he's not even an example of it. He seems to do well for his constituents. The problem is that people outside his state keep (stupidly) choosing not to be his constituents.
