I feel like the only characteristic needed to be a popular speaker is self-confidence. Have you seen most of the word salad coming out of Trump's mouth?
It’s word salad, but for his demographic, it’s a salad of carefully selected words they love, delivered with great warmth, charm, or aggression, as appropriate.
All of his 'success' is purely derived from charisma as far as I can tell. He isn't particularly adept at his prior career of real estate business given that he has under-performed in the markets he has participated in, and he had to commit felony fraud to do it. His biggest success is making people believe that he is more successful than he is.
What intellectually rigorous activity would you say he has an aptitude in?
Looking at the wildly hostile media coverage of him post-2015, you’d come away thinking he’s a major charlatan.
Looking at the glowing media coverage of him pre-2015, he seems like a unique business genius.
The truth is probably in between.
Business and marketing aren’t rigorous intellectual activities like math, but they are bloody hard in a different way - even with an inheritance (how many born-rich kids die 100x richer? Almost none). The problems are very fuzzy and open-ended, and frequently don’t even look like a problem.
You can’t consistently solve these problems profitably over many years without some skill.