Um, the Court Case Could Be The Least of Your Worries...

I'm genuinely trying not to be crass here, but on earth is this?

Unless a handful of wavering Democrats change their minds, the Republican-controlled Missouri legislature is expected to enact a statute next month nullifying all federal gun laws in the state and making it a crime for federal agents to enforce them here. A Missourian arrested under federal firearm statutes would even be able to sue the arresting officer.

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What distinguishes the Missouri gun measure from the marijuana initiatives is its attempt to actually block federal enforcement by setting criminal penalties for federal agents, and prohibiting state officials from cooperating with federal efforts. That crosses the constitutional line, said Robert A. Levy, chairman of the libertarian Cato Institute’s board of directors — a state cannot frustrate the federal government’s attempts to enforce its laws....

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Gary Marbut, a gun rights advocate in Montana who wrote the Firearms Freedom Act, said that such laws were “a vehicle to challenge commerce clause power,” the constitutional provision that has historically granted broad authority to Washington to regulate activities that have an impact on interstate commerce. His measure has served as a model that is spreading to other states. Recently, the United States Court of Appeals for the Ninth Circuit struck down Montana’s law, calling it “pre-empted and invalid.”

A law passed this year in Kansas has also been compared to the Missouri law. But Kris W. Kobach, the Kansas secretary of state, disagreed, saying it had been drafted “very carefully to ensure that there would be no situation where a state official would be trying to arrest a federal official.”

Yeah, I wouldn't be so much worried, if I was among the good people of Missouri, about a court challenge to the constitutionality of the bill. My worries would stem from the first attempted arrest of a federal official seeking to execute federal law. Because that sounds awfully like insurrection to me. In fact, Section 332 of Title 10 of the U.S. Code seems to agree:

Whenever the President considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings, he may call into Federal service such of the militia of any State, and use such of the armed forces, as he considers necessary to enforce those laws or to suppress the rebellion.

And section 333:

The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy, if it—
(1) so hinders the execution of the laws of that State, and of the United States within the State, that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law, and the constituted authorities of that State are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection; or
(2) opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.
In any situation covered by clause (1), the State shall be considered to have denied the equal protection of the laws secured by the Constitution.

(My italics)

Is it constitutional? Of course; it's called the Supremacy Clause.

Seriously, guys; not so much of a plan.