Given how determined Trump has been to keep this secret, it's more or less obvious that he's been hiding *something* -- and, before anyone suggests that no, he's just protecting private interests: he should have abandoned that right when he became President, the ultimate servant of the people. The people (in the US at least, although by extension everywhere) have an implicit right to know who their leader is, how they made their wealth, etc etc. This is why the convention about releasing tax returns came about, and why it was always abhorrent that Trump broke that convention (and then lied about why he was breaking it).