Fifty years ago, President Richard Nixon signed into law the Postal Reorganization Act, the landmark law that created the United States Postal Service (USPS). The law walked a difficult tightrope—creating a postal network that operated as both a business and public service. Today, as the fate of the USPS hangs in the balance, we’re featuring an excerpt from “Letters, Power Lines, and Other Dangerous Things: The Politics of Infrastructure Security” that looks back at the creation of the USPS and reveals how it transformed postal politics for good — and for ill.