From the May 7 edition of Fox News' The Story with Martha MacCallum:
MARC THIESSEN: Two things to take away from this. Number one those documents leaked. This is why Donald Trump does not want to release his taxes to Jerry Nadler because if they go up to Congress they are going to leak in the same way and he has no legitimate legislative reason for asking for these documents, he's on a fishing expedition.
Two, I always thought that the reason why Donald Trump doesn't want his taxes released is nothing to do with any corruption or illegality, it's because they're going to show he's not as rich as he says he is because when you do your taxes your incentive is to minimize your income as much as possible to pay the least amount of taxes. So Donald Trump has the best accountants in the world, they're going to organize his finances in a way to minimize his income.
The New York Times: Decade in the Red: Trump Tax Figures Show Over $1 Billion in Business Losses