GUN!

(State law is not applicable and neither state or local government can legally bring charges)

I'm surprised to learn this. I'm assuming this is only when the actions in question take place during an official operation?

The Supremacy Clause article VI section 2 covers this 

In a nutshell federal law enforcement in the performance of their duties are subject to federal law and not local/state laws

Like how California can say it’s illegal for ice to cover their face….but that law doesn’t mean anything due to the supremacy clause