WASHINGTON (AP) — White House national security adviser Mike Waltz is set to depart the administration, according to two people familiar with the matter on Thursday, marking the first major staff shakeup of President Donald Trump’s second term.

Waltz was among high-ranking members of the administration who accidentally shared plans about a forthcoming U.S. military attack with the editor of the Atlantic magazine on the messaging app.

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