Trump added that acting secretary Patrick Shanahanmay remain in the post for the foreseeable future, Army Times reported.
Shanahan currently serves as the deputy secretary of defense at the Pentagon, the No. 2 civilian position there, which has traditionally focused more on the internal workings and business practices of the Defense Department.
Trump announced on Sunday via Twitter that Shanahan would immediately replace Mattis after the departing defense chief released a public resignation letter last week citing his differences with the administration’s security policies.
Instead, Shanahan will immediately take the reins and Shanahan "could be there for a long time" in the acting defense secretary position, Trump said, according to Reuters, during his surprise visit to Iraq yesterday.