For Democrats starving for a villain in post-Trump Washington, Louis DeJoy seemed like an ideal candidate for the role. As postmaster general, he’s the most powerful holdover from the previous administration—a Trump campaign donor and logistics executive hired to run the cash-strapped U.S. Postal Service. When DeJoy moved last summer to slow the mail, his critics charged that he was carrying out a Trump plot to help steal the presidential election and degrade a beloved American institution. DeJoy’s critics, however, were fretting about the wrong crisis. The Postal Service handled th...