A big part of the problem for the post office is that even though they are a corporation, they cannot adjust the organization and business practices to meet market influences and stresses without going through congressional approval. They are this weird carryover from times past where postal deliveries were classified as critical to the nation and given special protections, but lost all flexibility, and the special protections are for things that no longer exist. A normal government agency gets an ever deepening pot of money to cover the new and burgeoning regulatory requirements. The post office has to beg to raise the price of stamps to try and keep up.

That concept that the post office is critical to national security is pretty much gone at this point. Immediate matters are handled through secure email. Critical documents are more trusted to FedEx. Technology and modern capability has passed up the post office. The question now is how long will it hang around before it disappears.