"But he's a rich celebrity who can say that he's built a business for himself."
In which bizarre parallel universe is this? Donald J. Trump inherited his wealth from his father who made his money by working interesting angles on government housing programmes in ways that seem at the very least "questionable" in the sense of "Someone should have been asking questions at the time these deals were agreed."
It is often stated that Donald J. Trump has made a fortune in property by starting out with a much bigger fortune that he inherited from his father. If he had invested that money in a managed fund he would have much more money than he does today.