Also he stole millions from his late brother's estate when he died, and was thus always able to lawyer-up, sue and outlast business opponents/vendors he cheated in deals, but IMO he's shown signs of losing it mentally.

I lived in NY in the late '70s thru the '00s when he was younger and making spectacularly stupid financial moves, plus the attention-grabbing ones he did to stroke his ego/get women, but he also did some things that weren't stupid, like when he took on and quickly refurbished the Wollman Skating Rink in Central Park that the Koch Admin had bungled for years.

That got everyone's attention, and along with the Trump Tower building, it made him seem like someone who knew how to get things done.

The tearing down of the Bonwit Teller building, with its Art Deco frieze masterpiece, to build his gaudy tower was a disappointment to architecture observers though. The casino failings and other business fiascos were still to come, as were his grooming by the Russians, his political ambitions and the increasingly apparent mental acuity/sanity lapses of the 2010s to now.

Remember, his father also suffered mental decline in later years.