Temporarily Filling Presidentially Appointed, Senate-Confirmed Positions [April 18, 2017] [open pdf - 516KB]
"A vacant presidentially appointed, Senate-confirmed position (herein, 'advice and consent position') can be filled temporarily under one of several authorities that do not require going through the Senate confirmation process. Under specific circumstances, many executive branch vacancies can be filled temporarily under the Federal Vacancies Reform Act of 1998 or by recess appointment. In some cases, temporary filling of vacancies in a particular position is specifically provided for in statute. Generally, designation or appointment under one of these methods confers upon the official the legal authority to carry out the duties of the office. Alternatively, an individual may be hired by the agency as a consultant. A consultant does not carry the legal authority of the office, and may act only in an advisory capacity. In many instances, the functions of a vacant advice and consent office may be carried out indefinitely by another official, usually the first assistant, under the terms of an administrative delegation order of the agency head. In such instances, the official carries out these functions without assuming the vacant office."
CRS Report for Congress, RS21412
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html