Acting Defense Secretary Patrick Shanahan is not moving forward with the confirmation process to take the job permanently, President Trump announced on Tuesday.
Trump said that Mark Esper, who now serves as secretary of the Army, will succeed Shanahan as acting secretary of defense, but did not reveal whether Esper would be nominated for the permanent job.
Trump said the Secretary of the Army, Mark Esper, will be named as the new acting defence secretary.
Trump appointed Shanahan, a former Boeing executive, to acting secretary last December after James Mattis stepped down.
In a statement announcing his resignation, Mr Shanahan called it "unfortunate that a painful and deeply personal family situation from long ago is being dredged up and painted in an incomplete and therefore misleading way".
"In response to a request from the US Central Command for additional forces, and with the advice of the Chairman of the Joint Chiefs of Staff and in consultation with the White House, I have authorized approximately 1,000 additional troops for defensive purposes to address air, naval, and ground-based threats in the Middle East", Shanahan said in a statement.
Shanahan, who grew up in Seattle, was nominated and confirmed as deputy defense secretary in 2017. "I know Mark, and have no doubt he will do a fantastic job!"
Under the Federal Vacancies Act of 1998, the president can appoint an acting defense secretary without immediately getting Senate confirmation, but this acting secretary can serve in that role for only 210 days before a nomination for their confirmation is given to the Senate. "Esper also served as the Legislative Director and Senior Policy Advisor to Senator Chuck Hagel", the bio said.
He is a 1986 graduate of the U.S. Military Academy at West Point and spent 21 years in the Army, rising to the rank of lieutenant colonel before retiring from the Army Reserves in 2007.
Democratic Sen. Richard Blumenthal of CT, who serves on the Senate Armed Services Committee, told reporters the committee was not informed of Shanahan's domestic history when he was nominated and confirmed as deputy secretary in 2017.
As Army secretary, Esper has focused on building combat readiness as the service has shifted its focus to prepare for major combat operations in the case of a war with a near-peer power competitor such as Russian Federation or China.