Charisma is strength of personality, largely. The ability to properly use your charisma is a question of intellect.

The perfect example was Hitler (as much as I hate to use an example used by everyone for most things). The man was charismatic, and he was known for his stirring speeches. His propaganda campaigns (often perfected by associates of his) helped sway others to his cause.

Everything has a role in their rise to power, but you always want a charismatic figurehead that will touch others.