I'm by no means in the business of defending Trump, but the $400 million of debt is NOT abnormal. They're simply real estate loans he's personally guaranteed. He's not the borrower, he's the guarantor.
I'd like to know why he personally guaranteed them and if there are any other guarantors, but the mere fact a real estate investor has personally guaranteed a lot of his portfolio's debt could be totally benign.
The rules around the presidency simply don't account for a guy with such a complex portfolio of assets and liabilities, so there isn't a robust process around thoroughly vetting who Trump owes money to.