Kevin McAleenan, the acting secretary of the Department of Homeland Security (DHS), surprisingly resigned on Friday, October 11.
McAleenan, who had previously served as commissioner of Customs and Border Protection (CBP), held the position for only six months.
It is not known at this time who will replace him.
McAleenan is the fourth person in the position since Trump's presidency began.
McAleenan replaced Kirstjen M. Nielsen, who resigned in April after 16 months. Nielsen took the reins from Acting Secretary Elaine Duke. General John Kelly formerly headed DHS for six months before being appointed as secretary to the presidency.