Arrest them and prosecute them, what they are doing is illegal, without permission from local government. Will they have the balls, only time will tell. Feds get real weird when they are arrested and cannot bully you into submission to cooperation. We are taking over this investigation, Excuse me, no your not and if you ( feds ) get in our way we will arrest you and put you in jail.
Tom you are right, Sheriffs are elected not hired, and have county jurisdiction and don't have to answer to anybody unless they are doing something illegal, then the deputies can arrest the Sheriff.
If anybody has the time and I do mean time, thousands of pages, read article 18 of the interstate commerce clause, the feds do no have the right to mess in city, county or town business, only on their own property or property ceded to them.