Elaine Costanzo Duke is an American civil servant and former United States Deputy Secretary of Homeland Security, serving from April 10, 2017 until April 15, 2018. She became acting Secretary of Homeland Security on July 31, 2017, when John F. Kelly assumed the office of White House Chief of Staff. She left the acting position on December 6, 2017, upon the confirmation of Kirstjen Nielsen.