This wasn't 'his' money as if he lost money out of his account. The money he lost was business losses, losses that were based on highly debt leveraged buildings (a lot of which was double and triple leveraged from his prior 1990 multi-billion dollar bailout). Also with his losses were taxpayer money, up to 1.8 billion in bond offerings New Jersey had to cover off his Atlantic City properties. The 1 Billion number is his share of those loses that he shifted to his personal tax statements but they are part of much larger business losses.
He has run his businesses like a guy who runs up credit cards, then gets more credit cards to make minimum payments on the ones he maxed out, then he continues that over and over until he can no longer get credit, then he gets bailed out or goes bankrupt and starts over again- lather, rinse, repeat.
This was 'his money' like a teenage girl running up her daddy's credit card is spending her money... technically no, it is your daddy's money but also, being drawn on a bank loan so it is the bank and her customer's money.