Why do we (our society) keep electing these sorts of people?
It is also something that can be prepared by other people, considering that another commenter has pointed out that he comes from a political family, it could be that this was prepared for him for exactly this purpose.
It could simply be the genius of the political machine. When you have systems and multiple people in place, it's hard to assess individuals. Clearly someone is, we just don't know who. But from that perspective, the representatives are often not where the intellectual heavyweights with the real decision making either.
Maybe I'm misunderstanding your argument here.
Bernie Sanders and Hillary Clinton gathered large bases because of what they were saying, but not because of how they said it. Rather than instilling confidence by charisma, they had to convince people of their abilities. In a way, that's much harder. Charisma is a bit like a cheat code.
You can also see this in Bill Clinton, who despite passing some dreadful legislation and being scandalized, people continued to have respect for, because he was very charismatic.