28 U.S.C. § 508

(a) In case of a vacancy in the office of Attorney General, or of his absence or disability, the Deputy Attorney General may exercise all the duties of that office, and for the purpose of section 3345 of title 5 the Deputy Attorney General is the first assistant to the Attorney General. (b) When by reason of absence, disability, or vacancy in office, neither the Attorney General nor the Deputy Attorney General is available to exercise the duties of the office of Attorney General, the Associate Attorney General shall act as Attorney General. The Attorney General may designate the Solicitor General and the Assistant Attorneys General, in further order of succession, to act as Attorney General.