If you were driving down the road and got pulled over by a man driving a Postal truck, he obviously would not have the authority to issue you a citation. The person issuing a citation must have the lawful authority to do so. Anyone that is authorized to issue citations has jurisdiction.
In Article I Section 8 of the Constitution for the United States the jurisdiction of the Congress of the United States is limited to a ten mile square plot of land known as the District of Columbia. Anyone living outside of that plot is not subject to the jurisdiction of the United States.
The Supreme Court has ruled that the county sheriff is not required by the Constitution to enforce the laws enacted by Congress or any Federal regulatory agency. The County Sheriff is protect the lives, liberty and property of the people living in his or her county against local criminals as well as those representing the Federal government.