Inspections have also extended to bus and train stops, where federal agents in Florida, Maine, New York and Washington State have recently asked riders about their immigration status.

While the agency’s name might suggest that its purview is limited to the immediate border, officers can work in any area within 100 miles of the perimeter of the United States. It is a wide swath of the country that is home to an estimated 200 million Americans and fully covers at least 11 states. Maine’s international borders with Canada and the Atlantic Ocean make the entire state open to immigration authorities.

It is difficult to determine how often the Border Patrol conducts highway checkpoints or stops riders at transportation stations. Customs and Border Protection issues news releases about the results of some of the stops but does not publish comprehensive details on how often they occur or how many people are stopped.

The nearly six-minute video of the Maine encounter offered a window into the reach and power of the Border Patrol at a time when its enforcement of the Trump administration’s “zero-tolerance” policy has come under intense criticism. The reporters asked a Border Patrol agent why the checkpoint had been set up.

“It’s just a random checkpoint. It’s within 100 miles of the border,” the agent said. “We just occasionally set them up to see what we can catch.”

The agent added that the officers look for signs that include how people answer their questions and if they speak with an accent. He argued the stops were fair and free of potential bias because every person who passed through the checkpoint was asked the same question.