U.S. President Donald Trump ousted his national security adviser Mike Waltz on Thursday and named Secretary of State Marco Rubio as his interim replacement in the first major shakeup of Trump’s inner circle since he took office in January.

Trump, in a social media post, said he would nominate Waltz to be the next U.S. ambassador to the United Nations, adding that “he has worked hard to put our nation’s interests first.”

Earlier in the day, multiple sources said Trump had decided to remove Waltz from his national security post. The retired Army Green Beret and former Republican lawmaker from Florida had faced criticism inside the White House, particularly after he was caught up in a March scandal involving a Signal chat among top Trump national security aides, Reuters reported.

Rubio will be the first person since Henry Kissinger in the 1970s to hold the positions of secretary of state and national security adviser simultaneously.

“When I have a problem, I call up Marco. He gets it solved,” Trump said at a White House event earlier on Thursday.

A person familiar with the matter said Trump wanted to get to the 100-day mark in his term before firing a cabinet-level official. News of the shake-up on Thursday was so abrupt that State Department spokesperson Tammy Bruce learned about it from reporters at a briefing.

The national security adviser is a powerful role that does not require Senate confirmation. Trump had four national security advisers in his first term: Michael Flynn, H.R. McMaster, John Bolton and Robert O’Brien.

Waltz’s deputy, Alex Wong, an Asia expert who was a State Department official focused on North Korea during Trump’s first term, is also being forced from his post, two people familiar with the matter told Reuters.

The Waltz ouster caps a month of personnel turmoil within Trump’s national security establishment. Since April 1, at least 20 NSC staffers have been fired, the director of the National Security Agency has been dismissed and three high-ranking Pentagon political appointees have been shown the door.

The purges have seriously hurt morale in some areas of the national security establishment, according to several officials within or close to the administration. Some elements of the government are low on relevant national security expertise and in some cases it has proven difficult to attract high-level talent, the officials added.

The NSC is the main body used by presidents to coordinate security strategy, and its staff often make key decisions regarding America’s approach to the world’s most volatile conflicts.

Waltz was blamed for accidentally adding the editor of The Atlantic magazine to a private thread describing details of an imminent U.S. bombing campaign in Yemen. The Atlantic subsequently reported on the internal discussions about the strikes.

At a subsequent Cabinet meeting with Waltz in the room, Trump expressed his preference for holding such conversations in a secure setting, a clear sign of his displeasure. But he and others in the White House publicly expressed confidence in Waltz at the time.

Trump so far has expressed confidence in his defense secretary, Pete Hegseth, despite the turmoil at the top levels at the Pentagon and his involvement in the Signal controversy.

Waltz also attended Trump’s televised cabinet meeting on Wednesday. In a Reuters photograph from the meeting, Waltz appeared to be using the Signal app on his phone. The photograph appears to show a list of chats he has had on the messaging app with other cabinet members, including Vice President JD Vance and Intelligence Chief Tulsi Gabbard.

Commenting on the photo, White House communications director Steven Cheung said on social media: “Signal is an approved app that is loaded onto our government phones.”

WAVE OF FIRINGS

The NSC that Waltz will leave behind has been thinned by dismissals in recent weeks.

The bloodletting began a month ago, when Laura Loomer, a right-wing conspiracy theorist, handed Trump a list of individuals in the NSC she deemed to be disloyal during a meeting at the White House. Following that meeting, four senior directors were released.

Those four senior directors – who oversaw intelligence, technology, international organizations and legislative affairs, respectively – had a long history in conservative policymaking and no apparent animosity toward Trump, leaving colleagues puzzled by their dismissals, according to two people with direct knowledge of the matter.

Some NSC staffers were upset that Waltz did not defend his staff more forcefully, those people said.

Since then, more than 20 additional NSC staffers of various profiles have been let go, typically with no notice, the people said.

The Signal controversy was not the only mark against Waltz in Trump’s eyes, sources said.

A person familiar with the Cabinet’s internal dynamics said Waltz was too hawkish for the war-averse Trump and was seen as not effectively coordinating foreign policy among a variety of agencies, a key role for the national security adviser.

Waltz’s ouster could be of concern to U.S. partners in Europe and Asia who have seen him as supportive of traditional alliances such as NATO and tempering more antagonistic views toward them from some other Trump aides, according to one foreign diplomat in Washington who spoke on condition of anonymity.

The U.N. position he is now being nominated for has been vacant since Trump withdrew the nomination of New York Republican Representative Elise Stefanik because her vote was needed in the House of Representatives, which is narrowly held by Republicans.