For example, in Printz v. United States, 521 U.S. 898 (1997) the Court held that the national government could not directly require state law enforcement officers to conduct background checks under the Brady Handgun Violence Prevention Act legislation.
For this reason, Congress has often avoided adoption of completely nationalized programs by one of two devices.
In the first, Congress creates a delivery system for federal programs in which the national government encourages local implementation of a federal program by providing significant matching funds.
The most frequent early use of the phrase may be found in a series of cases describing the paradigm for federally sponsored welfare programs such as medical assistance or the former Aid to Families with Dependent Children (AFDC) programs in which a participating state's program is financed largely by the Federal Government, on a matching fund basis, subject to federal mandatory regulations.
"While the federal system places limits on the ability of the national government to require implementation by a State executive branch, or its local political subdivisions, that limitation does not apply in the same way to State judicial systems.
In particular, unlike the civil regulatory context, cooperation threatens the constitutional rights of individual criminal defendants by allowing executives to circumvent local juries, judges, and laws.
Moreover, this cooperation also potentially weakens the ability of states and cities to function as political entities that can hold their law enforcement officers accountable in an area of traditional state police power ..."[2]