Every person I know that has charisma has something labeled WOO by the Gallup Organization. It stands for “Winning Others Over”. Here is the description:
Woo stands for winning others over. You enjoy the challenge of meeting new people and getting them to like you. Strangers are rarely intimidating to you. On the contrary, strangers can be energizing. You are drawn to them. You want to learn their names, ask them questions, and find some area of common interest so that you can strike up a conversation and build rapport. Some people shy away from starting up conversations because they worry about running out of things to say. You don’t. Not only are you rarely at a loss for words; you actually enjoy initiating with strangers because you derive satisfaction from breaking the ice and making a connection. Once that connection is made, you are quite happy to wrap it up and move on. There are new people to meet, new rooms to work, new crowds to mingle in. In your world there are no strangers, only friends you haven’t met yet—lots of them. Source
For those that have it, it strengthens them when in a situation where they can use it. They learn to become even better and more fluid at it. If they are lucky, they find a role where they can spend the bulk of their time being charismatic.
I suspect that it is much like @Adirondackwannabe says: you either have it or you don’t. For my friends that have it, it comes naturally. Some of us can pull it off for a short time, but it leaves us exhausted because it isn’t natural to our personalities.
@glenjamin That is an interesting observation. A co-worker, one who is an introvert, had test results showing that she has Woo. Working with people one-on-one, she could clearly get her message across and sell it. Put her in the front of a room to deliver the same message, and she became tongue-tied. There are different venues for utilizing charisma than just public speaking.