US President Donald Trump has fired Kristi Noem as secretary of the United States Department of Homeland Security and named Markwayne Mullin as her replacement.
Trump made the announcement on Thursday in a Truth Social post.
He said Noem would move to a new role as special envoy for a new regional security plan called the “Shield of the Americas”.
“I thank Kristi for her service at ‘Homeland,’” Trump wrote. He added that she had achieved “numerous and spectacular results (especially on the Border!).”
Mullin, a Republican senator from Oklahoma, is expected to assume office on March 31 if confirmed by the US Senate.
White House press secretary Karoline Leavitt said the administration will push for quick Senate confirmation.
The change is the first major cabinet-level reshuffle in Trump’s second term.
Noem, a former South Dakota governor, became one of the most visible faces of the administration’s immigration crackdown.
She often joined immigration agents during enforcement operations and strongly supported strict border policies.
Her leadership later faced criticism from some lawmakers.
Congressional officials questioned a $220 million government advertising campaign promoting border security that prominently featured Noem.
During a Senate hearing, Republican senator John Kennedy challenged the spending.
“It troubles me, quarter-fifth to a quarter of a billion dollars in taxpayer money when we’re scratching for every penny,” Kennedy said.
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When asked whether Trump approved the campaign, Noem replied: “Yes.”
Trump later told Reuters: “I never knew anything about it.”
Pressure on Noem also grew after two US citizens, Renee Good and Alex Pretti, were shot dead during encounters with immigration agents in Minneapolis.
Her comment that Pretti had “committed an act of domestic terrorism” before he was shot sparked backlash because it was made without evidence.
Democratic representative Pramila Jayapal criticised her leadership during a congressional hearing.
“DHS is supposed to be protecting our residents and upholding constitutional protections,” Jayapal said. “Yours is a case of failed leadership.”
Trump’s nominee, Mullin, has been a strong supporter of the administration’s immigration agenda.
Earlier this year, he defended federal immigration agents, saying:
“Obstructing federal law enforcement is a felony. Most Americans follow ICE instructions without thinking twice.”
After the announcement, Noem thanked Trump and said she was ready for her new assignment.
“The western hemisphere is absolutely critical for US security,” she wrote on social media.
“In this new role, I will build on the partnerships and national security expertise I developed over the last 13 months as Secretary of Homeland Security.”