"The nature of his businesses make it much more complicated than it would be if he worked sort of in a commodities kind of business, with a public corporation. But he has a family, private business surrounded by secrecy in markets that are not transparent," says Robert Weissman, president of the progressive watchdog group Public Citizen.
The issue is especially problematic because Trump has long done business with foreign buyers, especially those from Russia and China.
Reuters reported recently that at least 63 people with Russian passports or addresses had spent nearly $100 million buying real estate at seven Trump-branded properties in Florida.
Sometimes, those buyers have had what can best be described as shady pasts, such as David Bogatin, who was identified by U.S. officials as a member of the Semion Mogilevich organized crime family in the 1990s and once reportedly owned five condos in Trump Tower in Manhattan.