Article I appropriations / 1974 Impoundment Act bar.
documentedgovernment_studyPrivate Aerospace Contractors
Constitution + 1974 Impoundment Control Act bar spending on programs not disclosed to oversight committees.
Article I grants Congress the exclusive power of the purse; the 1974 Congressional Budget and Impoundment Control Act and National Security Act provisions bar the executive from spending appropriated funds on programs undisclosed to relevant oversight committees. This is the legal frame that would make Grusch's alleged routing not merely secret but unlawful if substantiated.