President Trump announced a major shakeup in his national security team Thursday, tapping Mike Waltz to be his United Nations ambassador while Secretary of State Marco Rubio will fill Waltz’s former national security adviser post on an acting basis.

Waltz had faced criticism for mistakenly adding a journalist in a Signal group chat where war plans were discussed.

Secretary of State Marco Rubio has a new job title: interim national security adviser. President Donald Trump announced the development on social media Thursday after firing his previous national security adviser,