Although Mr. Trump donates his salary to the government, it is subject to income tax along with his other earnings. But because Mr. Trump’s overall income was negative, he did not owe regular income tax on any of it.
He was, however, still subject to the Alternative Minimum Tax, a parallel tax system that reduces the benefit of some deductions, preventing wealthy people from erasing their tax liability altogether. Most significantly, the A.M.T. formula disallowed $45 million in losses that Mr. Trump had carried over from prior years.