Not to nitpick, but the USPS hasn't directly received taxpayer-dollars since the 1980's. It's a completely independent entity of the US government. I think part of the issue is the lack of support from taxpayers/government. They can't keep up with increasing costs (gas, transportation, etc) and are charging more to try and offset the differences
So you're telling me that because it's an independent entity of the US government that loses 16 Billion dollars a year that's not added to the federal deficit in which at some point will have to be passed on to the taxper. I don't believe the problem is lack of support from the taxpayers/government rather the growing expense of pensions and healthcare costs for USPS employees and retirees.