By Priscilla Alvarez, Kristen Holmes, Annie Grayer, Lauren Fox

(CNN) — President Donald Trump said Thursday on social media he was firing Homeland Security Secretary Kristi Noem and would name Oklahoma Sen. Markwayne Mullin to replace her.

Trump thanked Noem for her service, saying in his Truth Social post she “has had numerous and spectacular results (especially on the Border!)” and that she “will be moving to be Special Envoy for The Shield of the Americas, our new Security Initiative in the Western Hemisphere.”

He said Mullin would take over the position March 31.

Trump loves watching Mullin on TV, aides said, which played a role in the president’s decision to tap him for the position. Trump has called Mullin following combative interviews to praise him and White House staffers have often dispatched the senator to do cable news hits around big moments for the administration.

Noem thanked the president in a social media post shortly after the announcement.

“The western hemisphere is absolutely critical for U.S. security,” she said, referring to her new position. “In this new role, I will be able to build on the partnerships and national security expertise, I forged over the last 13 months as Secretary of Homeland Security.”

Noem, who was tapped by Trump to helm DHS at the start of his administration, has faced growing scrutiny over her conduct in the position, including her alleged romantic relationship with her chief adviser, distribution of the windfall of cash the department has received — particularly for an expensive ad campaign that showcased her prominently — and her conflicting accounts over fatal incidents involving federal immigration agents.

Current and former Homeland Security officials had privately questioned how much longer the secretary would remain in the post following what they perceived as a series of missteps. Those include blindsiding the White House with a decision to pause TSA precheck during the current DHS funding lapse — a decision that was reversed within hours — and her responses during two congressional hearings this week.

Trump himself was angry with how the hearings went — particularly her assertion, which he denies, that the president was aware of her DHS ad campaign.

Since the fatal shootings of US citizens Renee Good and Alex Pretti in Minneapolis, and Noem’s controversial responses, Trump has been asking allies about what they think of her. Those close to him believed at the time that it was largely Trump being Trump — he often asks about his team and how they are doing, particularly amid backlash.

CNN has previously reported that some top White House officials have long been frustrated with Corey Lewandowski, Noem’s top aide and the subject of some pointed questioning during this week’s congressional hearings.

Trump dispatched White House border czar Tom Homan to Minneapolis in January in the wake of the Good and Pretti shootings to resolve the issues on the ground there, an apparent rebuke of Noem’s handling of the situation. Homan and Noem have a long simmering feud and rarely speak, according to multiple current and former officials. White House officials maintained that the two were in lockstep with each other.

Problems on the Hill

GOP allies outside the administration had also grown weary of Noem — and support among GOP senators had weakened. That was evident in questions posed by Republicans during a Senate Judiciary Committee hearing this week.

“Quality matters, not quantity, quality, and what we’ve seen is a disaster under your leadership,” GOP Sen. Thom Tillis said at the hearing.

Republican Sen. John Kennedy confronted Noem about her agency’s advertising campaign, which, as Kennedy pointed out, often prominently showcases Noem. ProPublica reported last year that the recipient of a lucrative advertising subcontract was the husband of a former DHS spokesperson.

While Noem argued that bids for the advertisements were properly submitted, Kennedy said his research “shows that you did not bid them out” and, in one instance, chose a company that was formed “11 days before you picked them.”

“It troubles me, quarter-fifth to a quarter of a billion dollars in taxpayer money when we’re scratching for every penny and we’re fighting over rescission packages, I just can’t agree with Madam Secretary,” Kennedy said, later asking whether the president approved the campaign which featured her prominently.

“Did the president know you were gonna do this?” Kennedy asked.

“Yes,” Noem replied.

“He did?” Kennedy pressed.

“Uh huh, yes,” Noem said.

In an interview with Reuters Thursday, Trump denied knowing about the campaign. “I never knew anything about it,” he said.

Multiple other Republicans on the Senate Judiciary Committee, where Noem testified this week, wouldn’t say Thursday if they back her leadership, including Sen. Lindsey Graham, a close Trump ally.

“Time will tell,” he repeatedly answered when asked if he has confidence in the DHS secretary and if he would vote to confirm her again if he had the chance.

Complaints inside DHS

Homeland Security officials were stunned by the president’s announcement Thursday afternoon, though some saw her ouster as inevitable.

“I think it’s long overdue. She wasn’t qualified for the position from the beginning,” a Homeland Security official told CNN.

Another Homeland Security official said Noem “paid the price,” accusing her of exploiting the role for personal gain.

Officials in the department have been texting one another, sharing the news and trying to game out what comes next for the department. There was frequent turnover at the top of the agency during Trump’s first term.

Within DHS, officials had expressed increasing frustration — and at times, exhaustion — over the way Noem and Lewandowski, a longtime Noem confidante who was tapped early on to serve at DHS as a special government employee, run the agency.

“People are tired of their shit. Honestly, it’s been unreal,” one Homeland Security official told CNN.

Lewandowski, who’s only intended to serve in his role on a temporary basis, has developed a reputation at the department of reprimanding officials, directing the firings of personnel, requesting employees be put on administrative leave, calling agency leaders “to hold them accountable,” and micro-managing — including over the massive infusion of cash the department has received to ramp up deportations.

Noem downplayed his influence when asked by Republicans and Democrats about his role this week.

“His role is a special government employee. And special government employees work for the White House and the administration. There are thousands of them,” Noem said, maintaining that Homeland Security officials were following rules and regulations associated with special government employees in an exchange with Republican Sen. Chuck Grassley.

Noem was also grilled about longstanding allegations in the media that she was in a romantic relationship with Lewandowski. She called it “tabloid garbage” during a House hearing Wednesday.

Picking a longtime ally

Mullin told reporters Thursday afternoon that he’s spoken with Trump, but said they “still have to communicate” and “get on the same page.”

“So we’ll talk about it moving forward,” he said, adding that he has “no idea” how the confirmation process will go. The president had not indicated publicly if he intended to nominate Mullin to serve as a permanent replacement.

Mullin was elected to the Senate in 2022 after serving five terms in the House of Representatives.

In his tenure, Mullin has been a staunch ally of Trump and was a regular fixture in negotiations within his party, relying on his relationships across the Capitol to serve as a conduit between House and Senate Republicans. Over the summer, he was crucial in bringing Republicans together on passing the president’s landmark tax legislation, securing a deal with New York House Republicans on a state and local tax deduction.

As the chair of the Senate Appropriations subcommittee that funds the legislative branch, Mullin has been deeply involved in helping to improve lawmaker security in a heightened threat environment. A former Mixed Martial Arts fighter, Mullin is famous on Capitol Hill for intense workouts that he used to run for House members. He is often seen bouncing a ball during a long vote series or during tense negotiations.

In January, shortly after the killing of Pretti, Mullin told CNN he “absolutely” had confidence in Noem, though he said he hasn’t “had time” to see the viral videos of Pretti’s death.

Mullin has been working with the White House and Senate Democrats to try and find an end to the current DHS shutdown, while arguing that he does not want Congress to pass restrictions that would inhibit agents from doing their job.

A South Dakota return?

Some officials and sources close to the White House had mused, before Trump announced he was sidelining her, whether Noem would try to run for the Senate in South Dakota, challenging incumbent Sen. Mike Rounds in the GOP primary. To qualify for the ballot in South Dakota, Noem would need to gather just over 2,000 signatures before the filing deadline at the end of March.

But jumping in the race now wouldn’t give Noem much of a runway to campaign. The primary is scheduled for June 2, giving the former South Dakota governor less than three months.

Trump has also already endorsed Rounds for Senate and an effort to paint him as an instigator of the president would prove challenging. In his endorsement last year, Trump wrote on Truth Social that Rounds was “an America First Patriot” who had his “complete and total endorsement for re-election.”

“He will never let you down,” Trump said.

Unlike other Republicans on the ballot this year, like Maine Sen. Susan Collins or Louisiana Sen. Bill Cassidy, Rounds voted against convicting Trump in his impeachment trial in 2021. He voted for every one of Trump’s cabinet nominees and has rarely spoken out against Trump even though he is seen in the chamber as a pragmatic and more traditional Republican.

Rounds also voted for Trump’s signature tax package.

There was one notable squabble between Rounds and Trump. The president did vow back in 2022 that he may never endorse Rounds again after the South Dakota Republican called the 2020 election fair.

“I will never endorse this jerk again,” Trump said in a Truth Social post at the time.

This story has been updated with additional developments and reporting.

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