The difference is, the GAO has statutory conclusive authority to determine what the law requires, and neither the OMB nor any other executive agency do.
they are a congressional watchdog. they have the authority to determine what the law is for the congress, not the administration. this is, exactly what it has been for every administration, a policy dispute with the congress about what the law is.
of course it does. how else is he going to administer the law other than to determine what it requires? can he be wrong? hell yeah. thats what courts are for. to determine whoâs interpretation is more correct