Ellen Aprill and Lloyd Mayer have written this oped for TaxProf. It begins:

As the debate between the Vice Presidential candidates Wednesday night made clear, Donald Trump’s refusal to release his tax returns remains an important campaign issue. The extraordinary tax losses that Donald J. Trump reportedly had in 1995 emphasize the need for him to fully disclose his tax returns for all years from then forward. Without disclosure of his federal income tax returns, we cannot begin to evaluate fully his claim on Tuesday that he has “legally” and “brilliantly” complied with all of our complicated tax laws.

The ongoing tax issues relating to his foundation came to light only because of the required disclosure of those returns. Those issues — and the foundation’s failure to register to solicit charitable contributions that has now resulted in a cease and desist order from the New York Attorney General — seem to demonstrate a woeful ignorance of the applicable law or a complete disregard of it, either of which would be of even greater concern if also reflected in his personal and business tax positions. And at least one issue raised by the foundation’s tax filings can be resolved only with full disclosure of Mr. Trump’s personal tax situation.

The crucial issue, which the Washington Post has addressed in its careful reporting on the Donald J. Trump Foundation, is a principle that we tax lawyers call “assignment of income.” It is a tax doctrine that most citizens are unlikely to have encountered. It is important, however, because it prevents people from avoiding taxes.