If there's nothing to hide, Mr. Trump has nothing to fear. If there's something he fears the public knowing, then it potentially opens him up to corruption and blackmail. He is doing himself, his presidency, and the government at large a great disservice by refusing to divulge his tax returns. It reeks of the same air of clandestine subterfuge and misdirection that Mrs Clinton was (rightfully) accused of with regards to both Benghazi and her use of a private email server. For as long as he refuses to disclose the information people will always be asking, "what's he hiding?"