President Donald Trump fired Homeland Security Secretary Kristi Noem after criticism over her handling of immigration enforcement and disaster response.

He announced he would nominate Senator Markwayne Mullin of Oklahoma to replace her and named Noem as “Special Envoy for the Shield of the Americas,” a new security initiative.

Noem had faced intense scrutiny from Republicans over a $220 million ad campaign encouraging undocumented immigrants to leave voluntarily.

Mullin can serve as acting secretary while awaiting Senate confirmation, the AP has reported.

Noem addressed a law enforcement conference after the announcement without mentioning her dismissal and later thanked Trump on social media for her new role.