A lot of people think a customs officer spends their whole shift on the front line, in those little booths. That's not really true. There is a rotation around doing different functions, especially at a very busy border crossing point. That's a very contained space, especially in busy time periods with a backup of cars. That potentially is an extremely dangerous setting because of large numbers of people in close proximity.
In that scenario, what would the protocol be if it was a police officer in that booth, looking at a dangerous situation? What would be the primary objectives in a confrontation?