[DonaldDuke]

He was appointed to that "advisory" position specifically because he could not obtain the security clearances needed to serve as an official employee of the Department of Defense.

Source, please.

[Alberta's Child]

Source for what? It's no big secret that Perle could not obtain a high-level security clearance for the Pentagon. At the very least (in addition to the FBI investigation into his work as a member of Scoop Jackson's senate staff in the 1970s), his status as a dual citizen of the U.S. and Israel renders him incapable of obtaining such a clearance.