Conflict of Laws in Federalism

Federalism in the United States is a system of governance where power is divided between a central government and various regional authorities. This division of power can raise questions about which level of government has authority over specific policy areas. One important feature of this relationship is how the Constitution delineates responsibilities and powers between state and federal governments.

In this context, consider the scenario where a state passes a law regulating the sale of firearms that conflicts with federal laws. Which of the following principles best explains the outcome of this conflict?