agents and not fewer than 264 Marine and Air Interdiction Agents for southern border air and maritime operations. (d) Professional support staff Not later than September 30, 2024, the Secretary of Homeland Security shall hire, train, and assign sufficient professional support staff for the recruitment, hiring, training, and maintenance of the personnel authorized under subsections (a) through (c). (e) GAO report If the staffing levels required under this section are not achieved by September 30, 2024, the Comptroller General of the United States shall conduct a review of the reasons why such levels were not achieved. (f) Authorization of appropriations There is authorized to be appropriated $1,250,000,000 for each of fiscal years 2021 through 2024 to carry out subsection (a) though (d). 402. Establishment of workload staffing models for U.S. Border Patrol and Air and Marine Operations of CBP (a) In general Not later than one year after the date of the enactment of this Act, the Commissioner of U.S. Customs and Border Protection, in coordination with the Under Secretary for Management, the Chief Human Capital Officer, and the Chief Financial Officer of the Department of Homeland Security, shall implement a workload staffing model for each of the following: (1) The U.S. Border Patrol. (2) Air and Marine Operations of U.S. Customs and Border Protection. (b) Responsibilities of the Commissioner of CBP Subsection (c) of section 411 of the Homeland Security Act of 2002 ( 6 U.S.C. 211 ), is amended— (1) by redesignating paragraphs (18) and (19) as paragraphs (20) and (21), respectively