I think that the implementation will always be indirect in America (recommendations, in some of these cases, are actually the result of treaties).
Direct implementation would meet too much resistance. Look at how the UN controls Africa, it always has the surface appearance of being 'assistance' of some type to local authority (even in Africa where it wouldn't make a bit of difference to the people and where local 'authority' is a questionable term). It's the same here in the US in the relation of the Federals to the States: The Federal authority controls the States completely although the compliance is, theoretically, 'voluntary' and is implemented by the States with it's own police and courts in the guise of State law.
In a way, I wish the UN would get involved directly in controlling the US domestically, it would generate a resistance to their control that all but is non exist ant now.