In all fairness, I should start by pointing out that Frank Szabo is not running unopposed for the office of Hillsborough County Sherriff. Longtime incumbent James Hardy is opposing Szabo in the Republican Primary, and Democrat Bill Barry will be opposing Szabo or Hardy in the General Election.
Szabo does have some strange ideas which sadly are by no means unique to Szabo. He has picked up the endorsement of a former state party chair: sure that chair is Jack Kimball, but Kimball still has some influence.
Szabo's view of his office is, in his own words:
[T]he Sheriff is the Chief Law Enforcement Officer in the county and has no superior. The Sheriff is elected by the people and is answerable to them alone. No federal or state agency has authority in the county unless the Sheriff permits it. If, in the Sheriff’s opinion, a proposed action is unconstitutional, the Sheriff is duty-bound, and authorized, to block it.County Sheriffs across the country are beginning to re-affirm their role in the checks-and-balances embedded in our Constitutional Republic. In some western states, water rights are paramount. The federal Bureau of Land Management has informed some farmers that they must let their crops die; as they may no longer use their own water. Some County Sheriffs have evicted BLM agents from their county, thereby protecting the lives and property of the Citizens
Is there is anything in state law which gives the sheriff that much power? Nope. Are county sheriffs even mentioned in the state constitution? Yes, but nothing is said about what their powers are: the state constitution merely says that sheriffs must be elected and cannot be over 70 years of age. What about the U.S. Constitution? No, it doesn't even say anything about counties, let alone sheriffs.
Szabo has to make an historically inaccurate reference to English history to justfy his view of the county sherrif's power:
The Office of the County Sheriff dates back to at least 900 AD in England. The Sheriff had always been charged with protecting the rights and property of the sovereign. After the American Revolution, the Office of County Sheriff remained. At that point, it became the duty and authority of the Sheriff to protect the Rights and property of the Sovereign Citizens – from any unlawful action.
There are many problems with his argument, beginning with the basic fact that England as a unified political entity did not exist in 900 AD. The old English counties (which were essentially abolished in the 20th century) are not analogous to New Hampshire's 10 counties.
In case you're wondering, Szabo has no formal training as a police officer, lawyer, or even as a historian. He apparently has spent most of his career driving a limousine. His main qualification is that he thinks he is a Sovereign Citizen. However, there is no such thing as “Sovereign” citizenship in America.