What public policy does the case of McCulloch vs Maryland enforces?

The case of McCulloch vs Maryland established the supremacy of federal law over state laws. This principle is enshrined in the Supremacy Clause of the US constitution, which states that "This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding".

In the McCulloch case, the state of Maryland had imposed a tax on the Bank of the United States, a federal institution. The Supreme Court ruled that the tax was unconstitutional because it violated the Supremacy Clause. The Court held that the federal government has the power to create and regulate its own institutions, and that state laws cannot interfere with this power.

The Supremacy Clause is a fundamental principle of the US constitutional system. It ensures that the federal government can operate effectively and that state laws do not conflict with federal laws.