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Message to the ignorant...
This principle is established by the Supremacy Clause in Article VI, Clause 2 of the U.S. Constitution, which declares that the Constitution, federal laws, and treaties are the "supreme Law of the Land".
The Doctrine of Federal Preemption
When a state or local law conflicts with a federal law, the federal law prevails, and the lower-level law is deemed "preempted" or void.
Express Preemption: Congress explicitly states in a statute that it intends to override state or local laws.
Implied Preemption: Courts determine that Congress intended to take over a specific field (field preemption) or that the state law makes it impossible to comply with federal law (conflict preemption).
A similar dynamic exists at the state level: state law generally overcomes municipal (city or county) ordinances because local governments are "creatures of the state" and derive their authority from state constitutions or legislatures.
Federal officer carrying out lawful Federal laws/orders are exempt from State and Municipal statutes/laws.
So if the District Attorney for Philadelphia is making that statement. He'd better check with the Federal gov't.
He's blowing smoke and you're ignorant enough to believe him...