President Donald Trump says he is nominating national security adviser Mike Waltz as United Nations ambassador while Secretary of State Marco Rubio would take over Waltz’s duties on an interim role.

P resident Donald Trump is replacing his National Security Adviser, Mike Waltz, and nominating him to be Ambassador to the United Nations, he announced Thursday, marking the first major personnel shake-up of Trump’s second term.

Waltz was at the center of the Signal chat controversy, in which a journalist was accidentally included in a discussion of sensitive military information.