WASHINGTON — As the coronavirus emerged and headed toward the United States, an extraordinary conversation was hatched among an elite group of infectious disease doctors and medical experts in the federal government and academic institutions around the nation.

Red Dawn — a nod to the 1984 film with Patrick Swayze and Charlie Sheen — was the nickname for the email chain they built. Different threads in the chain were named Red Dawn Breaking, Red Dawn Rising, Red Dawn Breaking Bad and, as the situation grew more dire, Red Dawn Raging. It was hosted by the chief medical officer at the Department of Homeland Security, Dr. Duane C. Caneva, starting in January with a small core of medical experts and friends that gradually grew to dozens.