The Weird West
Each U.S. Territory has a single Federal Marshal, who serves as the chief law enforcement agent for the entire territory. One man (or rarely, one woman) to keep the peace across hundreds of square miles of wilderness and isolated settlements. The job tends to attract hard people, and even those get chewed up and spit out pretty quick.
U.S. Marshals can deputize others to assist in difficult situations, but only the Marshal is ultimately responsible for law and order. As a result, they tend to be on the road a lot.
Note that plenty of towns and cities like to call their local constables “marshals,” but town marshals are to U.S. Marshals as tinfoil is to cold steel. Don’t confuse the two, or you’re likely to regret it.