Signalgate was the national security adviser’s most glaring mistake. But his problems ran deeper. After Michael Waltz, the national security adviser, inadvertently included The Atlantic ’s editor in chief in a group chat about military attack plans on the Signal messaging app, he found himself on very thin ice with his boss.

Waltz's deputy, Alex Wong, who was also ousted this week, reportedly remains at the National Security Council.

President Donald Trump said Thursday that he would nominate outgoing national security adviser Mike Waltz to be the U.S. ambassador to the United Nations. Waltz, a former congressman from Florida, has been on shaky ground with Trump since March after he inadvertently added a journalist to a private chat on the messaging app Signal with other top national security officials to discuss military strikes in Yemen.