I imagine much of the negative net worth is actually huge jumbo mortgages on big fancy houses. Sure they can't afford them, but they get the best rates (with supporters buying the view lots next door, like Obama has) so in a sense it's just another too-good investment not available to ordinary citizens. Like Clinton's cattle futures.
"I imagine much of the negative net worth is actually huge jumbo mortgages on big fancy houses."
They've got to be upside down on it then, otherwise the value of the asset would exceed the debt, contributing to positive net worth.