28 U.S.C. § 562: Vacancies

(a) In the case of a vacancy in the office of a United States marshal, the Attorney General may designate a person to perform the functions of and act as marshal, except that the Attorney General may not designate to act as marshal any person who was appointed by the President to that office but with respect to such appointment the Senate has refused to give its advice and consent. (b) A person designated by the Attorney General under subsection (a) may serve until the earliest of the following events:(1) The entry into office of a United States marshal appointed by the President, pursuant to section 561(c). (2) The expiration of the thirtieth day following the end of the next session of the Senate. (3) If such designee of the Attorney General is appointed by the President pursuant to section 561(c), but the Senate refuses to give its advice and consent to the appointment, the expiration of the thirtieth day following such refusal.