April 1, 2020, 5:23 PM

On June 22, 2001, a group of well-known U.S. officials and a handful of senior policymakers gathered at Andrews Air Force Base in Maryland for a senior-level exercise that simulated a biological weapons attack—an outbreak of deadly smallpox—on the United States. Designed by the Johns Hopkins Center for Civilian Biodefense Strategies (now called the Center for Health Security) and the Washington-based Center for Strategic and International Studies (CSIS), the day-and-a-half-long “Dark Winter” simulation was conducted to gauge how senior leaders would respond to such an attack and included such high-level participants as Sen. Sam Nunn (who played the president), former White House advisor David Gergen (the national security advisor), and the retired career diplomat Frank Wisner (the secretary of state). But Dark Winter has since become legendary in senior policymaking circles in Washington for a different reason: It has regularly been cited by its designers and participants as the clearest exhibit of the spiraling stresses, and potential social collapse, that could be sparked by a public health crisis.