RON JOHNSON was supposed to be the genius retail mind who would save the declining department-store chain JCPenney. The veteran Apple executive had presided over the creation and rollout of that company’s spectacularly successful retail operations: Apple’s 300-plus stores are paragons of clean design and high-level customer service and boast sales-per-square-foot levels twice those of jeweler Tiffany. In the fall of 2011, William Ackman, the cocksure hedge-fund manager who had a 17 percent stake in JCPenney, recruited Johnson in the hopes he could do for the retailer what he had helped Apple do for electronic stores—turn a dowdy, low-margin no-hoper into an upscale money gusher.