From the Document: "On March 13, 2020, President Donald J. Trump declared a nationwide emergency under the Robert T. Stafford Disaster Relief and Emergency Assistance Act (the Stafford Act, P.L. 93-288 as amended), authorizing assistance administered by the Federal Emergency Management Agency (FEMA). Five days later, the President notified then-FEMA Administrator Peter Gaynor that the agency would assume leadership of the federal pandemic response effort--the first known instance of FEMA serving in such a role for a public health incident."
CRS Report for Congress, R47048
Congressional Research Service: https://crsreports.congress.gov/