Yes, I was ruminating on the phrase "Power tends to corrupt, and absolute power corrupts absolutely". It was spoken by Lord Acton, but was a rephrasing of William Pitt The Elder. At any rate, it appears to convey the message that power can be a corrupting influence (But not always), however, absolute power that is unchecked is always too much for human mortals.
I would agree that the presidential examples you gave did seem to be decent people, but we also need to remember that they didn't have absolute power. I think some seek power so they may effect change in the world that they believe is necessary or beneficial. Often, we equate power with money, and the landscape is littered with examples of it bringing out the worst in people. But then you also see others who have a generous heart, and it doesn't seem to change who they really are.
I wonder though, if you had the opportunity to have all power over everyone and everything, would you accept it? You would be godlike in authority. That would be a mighty sword for anyone to wield, and it would carry with it tremendous responsibility. In a sense, you would be able to shape the entire world (Metaphorically) to your desire. No doubt, someone with a self-serving desire would step up to the platform and dawn the badge without hesitation. It would scare the hell out of me, but why should it scare me, unless there is something inside that I don't fully trust.
Perhaps subconsciously, we realize that there is a human animal in all of us with it's primitive instincts for survival and desire for dominance. On the other hand, it seems the best antidote to power and corruption is humility. But how do you maintain that once everyone is intimidated by you? Nevertheless, if you didn't take the reins, it may fall into the hands of someone not so pure in heart, and you would know that you could have prevented it from happening.
Does true motivation and character always win out over power, or do each one of us have our limitations as to how much of anything we can ultimately handle. With power comes privilege, as well as intimidation. It would be a monumental challenge to use absolute power wisely. I think I would have a staff whose sole purpose would be to keep my ego corralled.