I thought he was rich enough to fund his own campaign..
He's not liquid enough. He has very little cash; most of his wealth (which he values at $10 billion, but Forbes values at $4 billion) is tied up in real estate and the leasing of his name.
Trump is also a high credit risk, so it's unlikely he could borrow enough to fund his effort.
No matter what the Trumpkins say, Trump clearly led everybody to believe he was going to fund both the primaries and the general himself. He never qualified anything in his speeches.
There's a lot of "fine print" with Donald Trump.