I would tend to disagree with this. Charisma is attained through certainty in one's cause. A charismatic person believes every word they say, they believe in the rightness of their goals, and they know how to explain it in a way other people can understand. All social skills can be learned, and charisma is one of those skills.
A charismatic person is secure in his convictions. He knows how to relate to people, but he makes his own ego secondary to the message. This is where a lot of politicians trip up. They make the message secondary to themselves. And while they might still win elections on cult of personality (or less scrupulous methods), they generally lack the ability to maintain a lasting popularity, even among their own supporters.
One of my favorite examples of a charismatic individual is Viggo Mortensen. He's an actor, writer, poet, photographer, painter, he speaks 4 languages, he's very affable and personable, dedicated to his work, a caring father... He's like an old-fashioned movie star. When he finished his last day of shooting for the Lord of the Rings trilogy, the stunt crew, who consisted primarily of beefy Maori rugby hooligans, were so taken with him that they performed a haka in his honor.
To be charismatic, think of it this way: at all times and in all ways, try to be more like The Most Interesting Man in the World.