President Donald Trump on Thursday said he was ousting Homeland Security Secretary Kristi Noem from that post and replacing her with Sen. Markwayne Mullin, an Oklahoma Republican.

Noem’s dismissal from the Department of Homeland Security comes after a wave of criticism of the former South Dakota governor’s management of the agency and her aggressive handling of Trump’s immigration enforcement agenda, which saw two American citizens killed by federal agents in Minnesota in January.

She is the first Cabinet secretary to be fired by Trump in his second term in the White House, which has been relatively quiet in turnover of top positions, in stark contrast to his first term.

Noem had been rumored to be on thin ice with the president, who likes to call the shots. Noem has been a headline name for the first year of the second Trump administration and has been a particular object of Democratic criticism. Trump fired her after a bruising hearing earlier this week when Republicans also piled on.

Trump announced Noem’s termination in a post on Truth Social, saying “The current Secretary, Kristi Noem, who has served us well, and has had numerous and spectacular results (especially on the Border!), will be moving to be Special Envoy for The Shield of the Americas, our new Security Initiative in the Western Hemisphere we are announcing on Saturday in Doral, Florida.”

“I thank Kristi for her service at ‘Homeland,’ ” added Trump, who plans to host like-minded Western Hemisphere leaders over the weekend to announce the security alliance.

Sen. Thom Tillis, R-N.C., during a hearing Tuesday where Noem was testifying, called her leadership of DHS a “disaster.”

“We’re an exceptional nation,” Tillis told her that day. “And one of the reasons we’re exceptional is we expect exceptional leadership. And you have demonstrated anything but that.”

Sen. John Kennedy, R-La., questioned Noem about a $220 million taxpayer-funded ad campaign about DHS border security, which included a Republican consulting firm with ties to Noem and DHS. The commercials prominently feature Noem, who, in some footage, is shown on horseback with Mount Rushmore in the background.

“Well, they were effective in your name recognition,” Kennedy said, after Noem defended the ads as being “extremely effective.

“It troubles me,” Kennedy said. ‘A fifth to a quarter of a billion dollars of taxpayer money when we’re scratching over every penny.”

Asked if Trump knew Noem was going to do the ad campaign, Noem testified, “Yes.”

But on Thursday, Trump told the Reuters news agency, “I never knew anything about it.”

At a hearing on Wednesday by the House Judiciary Committee, Noem, who is married, was asked if she had ever had sex with her top advisor, Corey Lewandowski, who is also married.

She refused to answer, calling the question “tabloid garbage.”

Noem, moments after her firing was announced, kept a speaking engagement in Nashville at the Sergeant Benevolent Association Major Cities Conference. She spoke calmly from behind a podium, taking questions about law enforcement logistics from a live audience and did not address her termination.

Noem did not address her ouster, nor did audience members who asked questions about DHS contracts and other more mundane matters. Trump spoke with her by phone before she took the stage, MS NOW reported. After the speech, she thanked Trump for her new special envoy role in a post on X.

Mullin would have to be confirmed as DHS secretary by the Senate to officially serve. But Trump said Mullin would begin serving in that post on March 31. Trump also could put Mullin in place in an acting capacity.

Tillis, who on Tuesday pledged to hold up Trump nominees over his concerns about how DHS was being run, won’t stand in the way of Mullin’s nomination, according to his office.

Mullin told reporters at the Capitol, “It’s an honor to be nominated.” He said he had also just received the news.

“We’re excited about it, excited to get to work, but we still got the nomination process,” Mullin said.

“We’re wanting to get the Department of Homeland Security working for the American people, and that’s going to be our focus,” he said. “And so we’re open to new ideas, doing things that, as I said, takes care of the job we need to get done.”

Mullin was elected in a special election to serve the remainder of the late Sen. Jim Inhofe’s, R-Okla., term, who retired mid-term in 2023.

He served in the House before his election to the Senate and was first elected in 2012. During his Senate tenure, Mullin has been a steadfast Trump ally and a top communicator for the Republican caucus. Mullin frequently holds court with reporters in the Senate hallways and is a regular on network television shows and cable news.

Mullin rose to greater prominence during negotiations over the massive 2025 Republican tax cut and spending bill known as “one big beautiful bill.” He served as an informal liaison between the House and the Senate during negotiations, helping to relay concerns between the chambers that are often at odds.

Mullin backed Senate Majority Leader John Thune in the race for the top job in the Senate. He is likely to get broad support from Republican senators and has already gained one Democratic supporter in Sen. John Fetterman of Pennsylvania. Senators tend to have an easier time during the Senate confirmation process, where they are voted on by their colleagues.

Democrats responded positively to Noem’s dismissal. House Minority Leader Hakeem Jeffries, D-N.Y., told reporters after Trump’s announcement, “Good riddance,” referring to Noem.

Jeffries, referring to Mullin, said, “I don’t have a comment right now on what’s to come.”

“A change in personnel is not sufficient,” he added. “Kristi Noem was a disgrace.”

Trump, in his social media post Thursday, lauded Mullin, calling him “a MAGA Warrior, and former undefeated professional MMA fighter” who “truly gets along well with people, and knows the Wisdom and Courage required to Advance our America First Agenda.”

“Markwayne will work tirelessly to Keep our Border Secure, Stop Migrant Crime, Murderers, and other Criminals from illegally entering our Country, End the Scourge of Illegal Drugs and, MAKE AMERICA SAFE AGAIN,” Trump said. “Markwayne will make a spectacular Secretary of Homeland Security.”

— CNBC’s Caleigh Keating, Justin Papp and Emily Wilkins contributed to this article.