The USPS is governed by, well, the government. The Republicans are actively looking to kneecap it, and as usual, the Democrats are doing basically nothing to stop them.
In my experience government services in areas completely controlled by Democrats don't seem better-run than ones in mixed-party or Republican-controlled areas. The "Starve the Beast" hypothesis doesn't seem to have much predictive value at the state and municipal levels, though I admit I haven't disproven it at the federal level.