FDR himself stressed the notion of limits as the flip side of largess with Social Security. “This act does not offer anyone an easy life,” he said in a 1938 fireside chat. It would “furnish that minimum necessary to keep a foothold; and that is the kind of protection Americans want.”

Indeed, Phillip Longman, in a provocative new book, The Return of Thrift, argues that Social Security was enacted largely to beat back costlier demands for universal old-age assistance championed by Francis Townsend, whose 10 million followers made him the one-man aarp of his day. Confining Social Security’s benefits to those who had first contributed payroll taxes was the ingenious way to limit government’s exposure, while giving Roosevelt the illusion of insurance he famously needed so that “no damn politician” could ever scrap his plan. In both senses, this “contributory” design worked. In 1940, less than 1 percent of the elderly received Social Security. Even as late as 1953, less than half the elderly got benefits, since they’d either retired before the system started …