Well.... Trump is claiming that his tax returns are still under audit years after the fact. Apparently they are still looking into 2009 (since Clinton released her tax returns from 1975-2015, what's keeping Trump from releasing his from 1975-2007?)
BTW, the answer to the question is shameless dishonesty.
That's kind of funny being you're a Democrat and your candidate has a history of shameless dishonesty. So much so that in the first Presidential debate when Trump challenged that she lacked stamina for the job of President, she shot back and referred to the 9+ hours she spent before a Congressional hearing to answer for her behaviors concerning Benghazi!
That's stamina in her book? She's partly responsible for the murder of American's in Libya, she's a liar about that, shameless dishonesty, and she's bragging that answering for it, when she really didn't because she's not yet in prison, is an example of her having the stamina to be President!
Truly! How twisted is that of her? Her shameless immoral depraved indifference to the plight of American's in Libya that led to their slaughter caused her to sit for 9 hours and more before a Congressional (political theater really is what it was) investigation committee to answer for that depraved behavior and she thinks that is a defense of the accusation she's lacking stamina?
Lady, you're lacking moral fiber and a conscience! Having stamina to defend that isn't a plus!
Meanwhile, back at the legal ranch, corporations regularly avoid paying federal income tax. It isn't illegal. That's why Trump rightly said, it is the law that let him to avoid taxes. If you want him to pay taxes, as he said, change the law.
Not likely that will happen.