and it came out during the campaign that he paid zero taxes for quite a number of years, based on earlier losses, so it's not that.

nor is it clear that russian ties or anything else would necessarily come out. he could just show interest expenses and not say to what source, e.g. he can release the returns without releasing all the supporting documents.

my suspicion has always been that he knows he is committing tax evasion and doesn't want eagle-eyed accountants across the country tipping off the irs.

unfortunately, he has always been so much in debt, owing more than he takes in, that the possibility of IRS charging him with failure to pay taxes on unreported income seems unlikely.