Kirstjen Michele Nielsen (/ˈkɪərstən/; born May 14, 1972) is an American attorney who served as United States Secretary of Homeland Security from 2017 to 2019. She is a former principal White House deputy chief of staff to President Donald Trump, and was chief of staff to John F. Kelly during his tenure as Secretary of Homeland Security.
Nielsen was confirmed as Secretary of Homeland Security on December 5, 2017. Nielsen is best known for implementing the Trump administration family separation policy. She resigned in April 2019.[1]