A County Sheriff is the highest law enforcement authority in his County. If any Federal law enforcement officer wants to conduct an operation in any County, he must do so with the permission and cooperation of the local Sheriff. After decades of Federal overreach, many County Sheriffs are stepping up to assert their authority. I see them as the best hope we have to reign in Federal power without violence and bloodshed. This is a good thing because once violence erupts, it could spread like wildfire. It could easily turn into a full-blown revolution.
Sheriffs take bold stand to protect citizens from federal overreach
http://www.wnd.com/2013/06/backlash-gun-control-laws-nullified/
The specific words may vary, but all law enforcement officers take an Oath of Office to support and defend the Constitution of the United States against all enemies, foreign and domestic.
CSPOA, or Constitutional Sheriffs and Peace Officers Association
10th Amendment: “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”
http://tenthamendmentcenter.com/about/about-the-tenth-amendment/#.Uaq275ywU2A