Donald Trump on Thursday announced that Kristi Noem will step down as Secretary of the United States Department of Homeland Security at the end of March.

Trump said he intends to nominate Markwayne Mullin to replace her, with the appointment expected to take effect on March 31, 2026.

“I am pleased to announce that the highly respected United States Senator from the great state of Oklahoma, Markwayne Mullin, will become the United States Secretary of Homeland Security (DHS), effective March 31, 2026,” Trump wrote in a post on Truth Social.

The president added that Noem, whom he said “has served us well,” will move to a newly created role titled “Envoy for the Shield of the Americas.” Trump described the position as one that will lead a new security initiative across the Western Hemisphere.

According to a person familiar with the matter, Trump spoke with Noem earlier Thursday about the change in roles. At the time, Noem was traveling outside Washington, D.C..

Earlier in the day, Mullin declined to answer questions about whether he had discussed the potential appointment with the president. The Oklahoma senator said he had spoken with Trump “recently” but added that he did not want to discuss the matter at the moment, saying, “We’ll discuss it later.”