"A recent shake-up in the leadership at the Department of Justice (DOJ) has brought to the fore a number of unresolved legal questions surrounding the President's ability to name acting officers. The controversy began on November 7, 2018, when then-Attorney General (AG) Jeff Sessions resigned at the President's request. As a position subject to the advice and consent process contemplated in the Appointments Clause of the Constitution, the AG's office will remain vacant until a presidential nominee is confirmed by the Senate. But in the interim, the President named Matthew Whitaker, the former AG's chief of staff, to serve as Acting AG, performing the duties of that office while it remains vacant. To install Whitaker as Acting AG, the President invoked the Federal Vacancies Reform Act of 1998 (Vacancies Act), a law that authorizes certain government officials to temporarily perform the duties of most executive offices that require Senate confirmation."
CRS Legal Sidebar, LSB10217
Congressional Research Service: https://crsreports.congress.gov/