We have very strong state governments in this country. Our constitution is pretty explicit about that. It lists the powers of the federal government, not a terribly long list, and explicitly states everything else is up to the states. Including jurisdiction on nearly all violent criminal acts within their state borders. The Supremacy Clause gives feds immunity ONLY if acting within the scope of their official duties. Beating the shit out of people, particularly US citizens, and violating their civil rights isn't within those official duties.
If they break state laws in that regard, arrest and indict them. If the regime wants to fight that, OK, we'll see them in court. In the meantime, federal thugs get prosecuted under state law. And incarcerated in state lock ups. Oh, won't that be fun. 
"But the feds will stop sending federal money!" Yeah, and they're not doing that already? Do you want us to simply lay down and let them tromp all over us? Oh, hell no.
Ever wonder why the Fugitive Slave Act failed miserably. That's because northern free states simply wouldn't have it. Sure, federal agents and others deputized for the purpose could attempt to enforce it in free states but they were hamstrung at every turn by state governments. And if they didn't like it, tough. Go pound sand. Filmore threatened federal invasion, but that was politically impossible and backed the hell off. Another blowhard, presidential failure. Southern states threatened secession over the lack of enforcement. If they want to do the same now...well...bye. You just saved us the trouble.
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