[robertpaulsen]

"I'm sure you can point to where in the Constitution, chapter and verse, the fedgov is authorized to do that."

I can.

Article VI, Clause 2. Supremacy Clause.

"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."

If federal law conflicts with state law, the federal law prevails.

[eno_]

Only if such a law ia authorized by the Constitution.

Is an unconstitutional law any law at all?

And, for extra credit, do you think federal LEOs are constitutionally authorized to roam wherever they please?