An investigation into Donald Trump’s real-estate holdings by The New York Times has called into question the Republican nominee’s claims of having great business savvy. According to the report, Trump’s companies are at least $650 million in debt—more than twice as much as he disclosed in financial forms for the presidential campaign. The discovery calls attention to how much of Trump’s finances remain a mystery, as he has refused to release tax returns or allow for any independent appraisal of his assets. In addition to the debt, Trump’s assets are also tied up in three passive partnerships owing an extra $2 billion to various lenders, the report said. The report mapped the financial web for 30 of Trump’s properties in the U.S., but much of Trump’s financial empire remained murky. “The success of his empire depends on an ability to get credit, to get loans extended to his business entities,” University of Minnesota Law Professor Richard Painter was quoted saying in the report. “And we simply don’t know a lot about his financial dealings, here or around the world,” he warned.