The Constitution says federal laws are "the supreme law of the land ," so the federal government could just take complete control.

The concept of federal supremacy does not equate to the federal government taking complete control over everything. Rather, it establishes that in areas where the Constitution grants authority to the federal government, federal laws and regulations supersede conflicting state laws and regulations. This principle is balanced by the fact that the Constitution limits the powers of the federal government, ensuring a system of checks and balances with the states. The states retain considerable autonomy under the Constitution, with the Tenth Amendment explicitly reserving all powers not specifically delegated to the federal government to the states or the people.