When we look at the lives of charismatic leaders, we always find that they have a sleazy side to them (usually involving their sex lives). When comparing, say, Kennedy and Rev. Jimmy Jones, some hypothesize a difference between good charisma and bad charisma. I would argue that there is no difference.
Every charismatic person (as described by others) I've ever seen instantly struck me as being sleazy, as incapable of being trusted. A sleazeball thinks he can lie himself out of any situation. A charismatic leader is simply a successful sleazeball.
Studies have shown that most of us are bad liars, giving ourselves away with inadvertent expressions or body language. However, a certain percentage of people become very good liars, capable of fooling even professional who deal with liars regularly (police, priests, parole officers, etc.). To the extent you rely on your people skills to detect liars, the more likely you are to be taken in by charisma.
"The Violent Male", van Vogt hypothesized a personality
disorder which consisted of being unable to admit a mistake (even
to oneself). One of the side effects of this affliction is a
charismatic personality. Another is a propensity toward violent
and/or self-destructive behavior when faced with an unavoidable
admission of error.
To the extent we believe that government can act as a force for good, we inevitably have unrealistic expectations for our leaders. What we want is someone with the wisdom to know the best course of action to achieve a desired goal, the empathy (actually, telepathy) to know our own best interests, and the virtue to put our interests above his own. Since there is no one like that, what we wind up voting for is the best liar.