That's odd. The online version of the Oxford English Dictionary defines charisma in this way:

"1. noun, Compelling attractiveness or charm that can inspire devotion in others."

Even by a brief dictionary definition of charisma, the term does not suit Trump. Trump has devoted adherents, as does any country's leader. But he does not have compelling attractiveness or charm. He's not a charismatic president. He's the antithesis of one. And when one fleshes out the notion of a charismatic leader into its common attributes, the term suits Trump even less. 

The above also speaks to why Trump was elected. Typically, America's political leaders ARE charismatic. They're charming, admirable, and attractive in so many ways. But Trump tapped into a current of public distrust in career politicians. Doing so helped bring him success. He would have had a hard time doing that if he seemed like every political leader.