The acting deputy secretary of the Homeland Security Department was forced to resign on Tuesday, the latest top-ranking official to be ousted from the agency.

Claire Grady stepped down from the post on Tuesday, officials said. As deputy secretary, she was next in line to replace DHS Secretary Kirstjen Nielsen, who was fired on Sunday.

Instead, President Trump tapped Kevin McAleenan to replace Nielsen, setting up Grady to either resign or be fired. She was forced to resign her post on Tuesday, two officials familiar with the decision told The Associated Press.

In two tweets on Tuesday evening, former Secretary Nielsen praised Grady for her leadership in the department.

“Claire has led the men and women of DHS who support our operational staff. Her sound leadership and effective oversight have impacted every DHS office and employee and made us stronger as a Department,” Nielsen wrote.

“I am thankful for Claire’s expertise, dedication & friendship & am filled w gratitude for her exemplary service to DHS & to our country. I wish her all the best in her future endeavors,” she added.

Trump has made changes in the agency in recent weeks because of his growing frustration with migrants crossing the U.S. southern border. After firing Nielsen, Trump said he wanted to pursue a “tougher direction” with his immigration policy.