President Trump announced on Thursday that he was removing his national security adviser, Michael Waltz, nominating him as ambassador to the United Nations and installing as his interim replacement Secretary of State Marco Rubio, who will remain the nation’s top diplomat.
It is the first significant personnel overhaul of top White House aides, and the kind of shake-up that Mr. Trump had sought to avoid in his second term.
“From his time in uniform on the battlefield, in Congress and, as my National Security Advisor, Mike Waltz has worked hard to put our Nation’s Interests first,” Mr. Trump wrote in a post on social media. “I know he will do the same in his new role. In the interim, Secretary of State Marco Rubio will serve as National Security Advisor, while continuing his strong leadership at the State Department.”
Mr. Waltz had been on thin ice as national security adviser for months, but his position became more precarious after it became public that he organized a group chat on the commercial messaging app Signal to discuss a sensitive military operation in Yemen and accidentally included a journalist in the conversation.
Most of Mr. Trump’s advisers had already viewed him as too hawkish to work for a president who campaigned as a skeptic of American intervention and eager to reach a nuclear deal with Iran and normalize relations with Russia.
Mr. Waltz’s deputy, Alex Wong, who worked on North Korea issues in Mr. Trump’s first term and who is considered a more moderate Republican with substantial national security experience, is also expected to be removed, according to a senior administration official with knowledge of the situation. The official and others spoke on the condition of anonymity to describe the internal discussions.
Mr. Rubio will now hold both positions, something that no other official has done simultaneously since Henry Kissinger held both titles under the Nixon and Ford administrations. Mr. Rubio has also been serving as the acting head of both the gutted U.S.A.I.D. and the National Archives.
Tammy Bruce, the State Department spokeswoman, learned of Mr. Rubio’s new role during a briefing with reporters, after Mr. Trump posted about it.
One person with knowledge of the discussions said Mr. Rubio had indicated some time ago that he would be willing to serve for roughly six months if Mr. Waltz was being replaced and Mr. Rubio was asked.
The Kissinger experiment has not been considered a success by most historians because the national security adviser is supposed to help adjudicate among competing arguments inside a national security establishment, and thus must often resolve differences among the State Department, the Pentagon and the intelligence agencies, among others. Mr. Kissinger was ultimately removed from the post of national security adviser and replaced with Brent Scowcroft.
But Mr. Trump is not running a second administration that has much of a true historical parallel.
Mr. Rubio ran against Mr. Trump in 2016, but they have developed a close working relationship in recent months, according to several top administration officials. Mr. Waltz is being provided a soft landing and praise as he departs the current role, while filling a spot left open when Mr. Trump abruptly pulled his nomination of Representative Elise Stefanik, Republican from New York.
The selection of the next national security adviser will be a critical one, at a moment when the president’s top national security and foreign policy aides have differed sharply on how to handle three of America’s most potent adversaries: China, Russia and Iran.
Mr. Trump is making the change just two weeks before his first major trip abroad, to Saudi Arabia and other Arab capitals in the Middle East, and in the midst of tense negotiations with Moscow and Tehran. Mr. Waltz joined him in Rome a week ago, for the funeral of Pope Francis, and was in the background of the meeting in St. Peter’s Basilica with Volodymyr Zelensky, the president of Ukraine.
Mr. Waltz, a veteran who had favored a muscular U.S. foreign policy for many years before Mr. Trump’s rise, had struggled since even before Mr. Trump’s inauguration to prove his bona fides to his base.
He also barely had time to organize a staff, much less tackle the hardest issues facing the president. Ordinarily a new national security adviser writes the administration’s national security strategy, often a yearlong process that involves hashing out differences among government agencies and cabinet members.
On some major issues — including how to engage China on its ambitions in the Indo-Pacific, its fast-growing nuclear program, its sophisticated cyberattacks on the United States and its allies and its effort to reunite Taiwan with the mainland — the administration has barely gotten started.
On Thursday morning, just as word of his ouster was beginning to circulate in national security circles in Washington, Mr. Waltz appeared on Fox News. It is unclear whether he knew then that he was being removed.
Mr. Waltz, who never made the public evolution toward Mr. Trump’s foreign policy views that Mr. Rubio did over the past several years, has been arguing internally for sharp sanctions against Russia if it fails to agree to a cease-fire with Ukraine. Mr. Waltz made that suggestion as an option for handling Russia as recently as Monday at a meeting with the president and senior members of his national security team.
So far, Mr. Trump has been reluctant to take anything but symbolic action against Russia, though at times he has threatened on social media to impose sanctions and tariffs.
And Mr. Waltz has been under siege by external allies of Mr. Trump for weeks, including the far-right activist Laura Loomer. Ms. Loomer had prompted the president to have Mr. Waltz fire several National Security Council staff members for what she perceived as disloyalty to Mr. Trump. Ms. Loomer had also aggressively targeted Mr. Wong.
Mr. Trump has been loath to fire anyone from cabinet-level positions since he took office a second time, seeking to avoid the headlines about the chaos that engulfed his first term.
Mr. Trump fired his first national security adviser, Michael T. Flynn, within four weeks of his inauguration in 2017, saying he did so because Mr. Flynn, a retired lieutenant general, had lied to Vice President Mike Pence about talks he held with the Russian ambassador.
Mr. Trump ran through four national security advisers in his first term. One of them, John R. Bolton, wrote a memoir about his time working for the president that was deeply revealing, and embarrassing, to Mr. Trump.
In his second term, Mr. Trump has appeared interested in avoiding not only headlines about the chaos, but also alienating people who could become vocal critics.
Discussions about replacing Mr. Waltz have been occurring in private for weeks, intensifying after the leaked Signal chat.
