Used N95 masks are collected at Boston's Massachusetts General Hospital on April 13. Hospital staff members wrote their names on the masks so each could be returned after being cleaned, a strategy used to alleviate critical shortages of respirator masks. (Blake Nissen/Boston Globe via Getty Images) The Strategic National Stockpile, which the U.S. has traditionally depended on for emergencies, still lacks critical supplies nine months into one of the worst public health care crises this country has ever seen, an NPR investigation has learned. A combination of long-standing budget shortfalls, l...