As the article you linked says, they're underfunded because the investments didn't perform as well as expected.
If there's something else to it, by all means feel free to state precisely the difference between how these pension funds from the random article you googled operate, and the USPS's requirements. There might be, but the article you linked doesn't imply that.
If there's something else to it, by all means feel free to state precisely the difference between how these pension funds from the random article you googled operate, and the USPS's requirements. There might be, but the article you linked doesn't imply that.