The supremacy clause, found in Article VI of the U.S. Constitution, establishes that federal law takes precedence over state law. In the situation where Florida's law allowing Cuban cigars is challenged, it is expected that the law will be struck down if it conflicts with existing federal law, particularly given the federal restrictions on Cuban imports resulting from the U.S. embargo against Cuba.
The supremacy clause ensures that when a state law directly contradicts a federal law or regulation, the federal law must prevail, leading to the invalidation of the state law. Since the federal government has the authority to regulate foreign commerce and has imposed restrictions on Cuban goods, Florida's law would likely be seen as conflicting with federal laws, resulting in it being struck down. This ensures a uniform legal framework across all states regarding matters governed by federal law, such as trade and commerce with foreign nations.
This principle is key in maintaining the hierarchy of laws within the U.S., ensuring that no state can enact legislation that undermines federal policy, especially in areas critical to national interests, such as foreign relations and trade.