The argument here is that it's all shell games otherwise if the money isn't set aside - e.g. look at the broader trend with social security's solvency. With the way public funding has trended, it would not surprise me if any unfunded programs simply ran out of cash at some point.

There isn't an easy answer to balance the needs of existing liabilities (pension commitments) with financial operations - the problem with the USPS was (I believe) the catch-up funding required to meet funding requirements, and not the actual funding itself.