Department of Defense Directive 5210.55: Department of Defense Presidential Support Program [open pdf - 25KB]
This Directive: 1. Reissues reference (a) to update policies and assign responsibilities. 2. Is implemented by reference (b) prescribing the procedures for the nomination, screening, selection, approval and continued evaluation of DoD military and civilian personnel, and contractor employees assigned to, or retained in Presidential support duties.
Defense Technical Information Center (DTIC): http://www.dtic.mil/dtic/