The Congressional Research Service (CRS), in a Mar. 11, 2004 report entitled "Enforcing Immigration Law: The Role of State and Local Law Enforcement," offered the following:

“States and localities bear the primary responsibility for defining and prosecuting crimes. But beyond enforcing the laws or ordinances of their state or locality, state and local officials may also have the authority to enforce some federal laws, especially criminal laws. Immigration law provides for both criminal punishments (e.g., alien smuggling, which is prosecuted in the courts) and civil violations (e.g., lack of legal status, which may lead to removal through a separate administrative system). The states and localities have traditionally only been permitted to directly enforce the criminal provisions, whereas the enforcement of the civil provisions has been viewed as a federal responsibility with states playing an incidental supporting role.”

Mar. 11, 2004