President Donald Trump said on Thursday that he would replace embattled Homeland Security Secretary Kristi Noem with Markwayne Mullin, a Republican Senator from Oklahoma, following a week of contentious congressional hearings that intensified scrutiny of her leadership and the department’s handling of immigration enforcement.[time-brightcove not-tgx=”true”]Trump announced the change in post on Truth Social, saying Mullin would become Secretary of the Department of Homeland Security effective March 31. Noem, he said, would instead serve as “Special Envoy for the Shield of the Americas,” a role tied to a new regional security initiative his Administration plans to unveil this weekend in Florida.The decision marks one of the most high-profile personnel changes of Trump’s second term so far and the first time he has removed a cabinet secretary since returning to office. It follows another prominent shake-up earlier this year when Trump replaced his National Security Adviser Mike Waltz after the controversy surrounding a Signal group chat leak of sensitive war planning discussions.Noem, a former governor of South Dakota, had been a central figure in carrying out the Trump Administration’s aggressive immigration agenda, one of the top issues that Trump campaigned on. As head of DHS, she oversaw agencies responsible for border security, immigration enforcement and disaster response, and became the most visible public face of the Administration’s sweeping deportation campaign and crackdown along the southern border.[video id=8LZUDBK9 autostart="viewable" vertical video_text=Kristi Noem testifies in the Senate in her first appearance since Minneapolis protesters' deaths]But her tenure was marked by mounting controversies that eroded support inside and outside the Administration. Over the past several months, DHS has faced intense scrutiny after federal agents shot and killed two U.S. citizens during immigration enforcement operations in Minneapolis earlier this year, sparking protests and calls for investigations into the agency’s tactics.Read more: How Trump’s ICE Became an Agency in CrisisThe turmoil has coincided with a standoff in Congress over funding for the department. Its budget authority lapsed in mid-February, forcing a partial shutdown affecting agencies including the Transportation Security Administration, the Federal Emergency Management Agency and the Coast Guard, while Democrats have pressed the White House for changes to immigration enforcement practices as a condition for restoring full funding.Trump’s frustration with Noem escalated sharply this week after she appeared before congressional committees for oversight hearings. Lawmakers from both parties questioned her about a $220 million government advertising campaign encouraging undocumented immigrants to leave the United States voluntarily—a campaign that prominently featured Noem herself.At one point during questioning from Republican Sen. John Kennedy of Louisiana, Noem said the President had signed off on the ad campaign. The statement reportedly angered Trump, who said he had not approved the initiative.“I never knew anything about it,” Trump later said in an interview with Reuters.The firm that handled the ad campaign was connected to the husband of Noem’s former spokesperson, drawing further scrutiny. Noem defended the contract process, telling lawmakers that it had gone through a “competitive process” and was “all done correctly, all done legally.”During the hearings, Noem was also questioned over her relationship with Corey Lewandowski, a Trump ally who ran his 2016 campaign and works as a special adviser at DHS. Noem and Lewandowski have both publicly denied rumors of an affair.Mullin, a close ally of Trump, served a decade in the House of Representatives before being elected to the Senate. Trump noted that he is a member of the Cherokee Nation and the only Native American currently serving in the Senate.“A MAGA Warrior, and former undefeated professional MMA fighter, Markwayne truly gets along well with people, and knows the Wisdom and Courage required to Advance our America First Agenda,” Trump wrote in his announcement. “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.”Before entering politics, Mullin ran a plumbing business and was a mixed martial arts fighter with a professional record of 5-0. He was inducted into the Oklahoma Wrestling Hall of Fame in 2016.Once formally nominated by Trump, Mullin is expected to face confirmation hearings in the Senate.This is a breaking news story and will be updated.