Very simple solution to this issue and many more like them.
Yes, the Feds can’t act on their own to enforce federal laws.
However, the FBI, DEA, ATF, US Marshals, ICE/HSI, rely heavily on local and state officers/deputies to fill the ranks of the many task forces set up around the country.
For example, the DEA isn’t all that big. Last I heard there were around 3000 agents. May seem like a lot but divide that up to 50 states, multiple offices, folks in admin-supervisory-training positions, whittling down the number of agents on the street doing enforcement. They rely on locals to fill those positions. Of course, the lure for the locals is the seizure money. You’re looking at, depending on location, somewhere in the neighborhood of $200-250k a year, per officer/deputy assigned, of seizure money going back to an agency. So, if an agency can afford to have 4 officers on a DEA task force, they could be looking at anywhere from $880 to over $1mil a year, into their bank account. And that money, which has stipulations about how it’s spent, can be used for all sorts of toys, gadgets, gear, training/trips, etc etc. Stuff that would not normally be paid for in the actual department budget.
So, if there is legitimacy to this state Congressman’s concerns, his constituent didn’t do anything wrong and this was just flexing from the ATF over some nonsense, pull all officer/deputies from the task forces. Make sure all the department heads are aware that any cooperation with the various federal agencies will be closely scrutinized and anything that is shown to have violated the rights of any citizen of the state will be investigated to fullest extent of the law. Make sure that it would be inadvisable for any member of state or local law enforcement to extend “professional courtesies” to any federal agent if/when they aren’t duty, on the way to an incident(feds can’t be cited if they’re working and en route to something...they can be cited if they just left Home Depot on a Saturday afternoon....yes they can use their take home car for that....after picking up some mulch).
Basically, stop helping them
Yes, under the 10th Amendment, States are empowered to do just what you describe. A check to the gross Federal actions that have no basis in Law.
States have power over Federals— who seem to have forgotten this, as have some States. It can change.