I think it takes someone of a certain mindset to drive themselves enough to get elected and be a leader, I think all leaders share some of the psychopathic tendencies that set them apart from the majority of people who are content to just follow someone elses directions and orders.
All leaders are ruthless and guileful by nature. The reason they are leaders is because they have the drive and the ability to exert their Nietzschean will to power over the weak. They are successful precisely because they have the tendencies of a sociopath: emotionless, calculating, cold and pragmatic. They will do whatever it takes
While I think that some people with psychopathic tendencies are attracted to being leaders, I think that most cases of such behavior is a by-product of their role. I think that some people are changed by their responsibilities. And some are tempted by the opportunities that are given to them to be corrupt.
When you're leading a group of people, you have a lot of responsibility. You make sure everyone does what they need to be doing, and you make sure that you continue being the leader. The psychopathic tendencies, or paranoia that leaders get is just a by-product of them trying to hold onto their role of leader.
I don't think of leaders as psychopathic, I think the closest they get to this is just from media portraying them as bad people. Leaders are taking on difficult positions with loads of stress, and to imply they are psychopathic is low. Normal people would break under far less pressure.