"In addition to congressional dysfunction, I am concerned with a growing leadership void within the department tasked with addressing some of the most significant problems facing the nation," Johnson, the chairman of the Senate Homeland Security and Governmental Affairs Committee, said in a statement on Monday.

In addition to Nielsen, CNN reported that White House adviser Stephen Miller is pushing for Lee Cissna, the director of United States Citizenship and Immigration Services (USCIS), and John Mitnick, the department's general counsel, to be dismissed.

A Trump administration official told CNN that there are also questions about the future of Claire Grady, under secretary of management at DHS.