I would say one of the barriers is that when you conduct pre-clearance activities, you want to ensure that whatever is pre-cleared is under control until it makes it to the border so that if a shipment is deemed customs-cleared, there is no possibility of introducing contraband into it. That's one of the big challenges and that's why we're working with industry to find ways to ensure that the goods won't be infected—if I can say that—before they make it to the border.
On September 20th, 2018. See this statement in context.