President Trump is nominating his national security adviser to serve as United Nations ambassador in a staff shakeup. Mike Waltz is being removed as national security adviser and has been tapped to represent the U-S at the United Nations. Meanwhile, Marco Rubio will serve simultaneously as Secretary of State and acting national security adviser. The president announced the personnel moves after news broke that Waltz was departing the White House. Waltz made embarrassing headlines in March when he mistakenly added a reporter to a Signal chat on military strikes.