The only way to prevent unfair competition is to open up bidding to all approved suppliers as of a cut off date which exists in the past. Should the volume of a given contract be great enough, then there might be more than one supplier. All terms for all qualified suppliers must be identical.
Protecion of "US only" suppliers in fact encourages non competitive pricing and is by definition "non competitive". Unfortunately, we have an ego maniac making "all" rules at the moment (who never worked a day in business) with a gigantic over sized ego and who owes US Unions and corrupt Union bosses big time for their political patronage.
Brian