THIS IS A SUMMER of milestones for America’s safety net. Ninety years ago this August—in the depths of the Great Depression—President Franklin D. Roosevelt signed the Social Security Act, which takes taxes from every paycheck to provide guaranteed retirement income for workers. Thirty years later, on another summer day, President Lyndon B. Johnson signed the law creating Medicare, the federal health insurance program for older Americans, also supported, in part, by payroll taxes. In polls, these two programs remain wildly popular. It’s not an exaggeration to say that these lifelines transformed aging in America.