Department of Homeland Security Secretary Kirstjen Nielsen has resigned, President Trump tweeted Sunday.
"Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service. I am pleased to announce that Kevin McAleenan, the current U.S. Customs and Border Protection Commissioner, will become Acting Secretary for @DHSgov. I have confidence that Kevin will do a great job!"
Behind the scenes: A source close to DHS told Axios that Nielsen would be having a showdown with the president on Sunday night.