When you consider the fact that he started with $413m, he actually isn't a great investor. Passively investing that money in the stock market (I know he wasn't given $413m in cash that he could have immediately put all in the market, but the principle still holds) since the early 80s would have yielded him much more than his current net worth, which supposedly is something like $3 billion. He's made 7-8x his money in about 40 years. The S&P is up almost 22x since 1980.
He certainly knows a hell of a lot more about business and the real world that other politicians, but his own track record on real estate investing is very mixed - he's had some stuff do really well and some stuff fail rather spectacularly, particularly his big miscalculation with his Atlantic City casinos.
Over time, there are few investments that outperform stocks.