Who is to enforce the Charter of the United Nations and The Universal Declaration of Human Rights ? The governments or the citizens of the member countries?
The Universal Declaration of Human Rights is generally a non-self-executing document which sets aspirational standards for member governments to adopt in the conduct of their affairs. Any enforcement is through the adoption of compliance constitutional and statutory provisions in the domestic law of a member nation and there is really no other way to enforce it. It may also inspire political action by citizens (or even a revolution) in cases where a member government does not comply, but those citizens receive no legal protections simply because they justify their actions in this manner.
An answer with respect to the U.S. situation in particular can be found here.
The Charter of the United Nations is enforced by the UN bureaucracy and UN representatives from various member nations in the conduct of the business of the United Nations.