For one thing, nobody knows how much money he had or has, let alone "made". We do know that he inherited about $400 Million through illegal schemes. Over a few decades, invested in the stock market, or almost anything else really, he could have been a totally unskilled billionaire. What he actually did, however, was to lose billions. There is indeed no apparent way he could have "earned" even a single billion, between all his failures. And no proof he ever personally owned a billion. He certainly seems in no rush to prove otherwise.

And you don't want to get me started on what lead to his electoral win. It certainly wasn't his smarts.