Preemptive self-defense is a large component of the US' security strategy. The US seeks to counter threats at the point of genesis rather than the point of commission. In the border context, the point of commission is the Port of Entry, which could be at the actual land/sea border or the functional equivalent of the border, such as an international airport located away from the actual border. Within US law enforcement, the DHS agencies, Customs and Border Protection (CBP) and Homeland Security Investigations (HSI), are uniquely empowered with border authority, which provides them more latitude to perform interviews and searches than the Fourth Amendment normally allows. Part of the CBP and HSI' "door step" strategy is the deployment of personnel to overseas locales in order to employ preventative programs at the point of genesis.
The above assumes that international engagement is a prerequisite of border security, premised mostly on the movement of people and goods for the promotion of commerce. It seems to me that a decrease in the reliance on imports and exports-that is, a more isolationist, insular economic policy-would better enhance border security, by lowering the probability that contraband and malevolent actors could cross US borders. If this hypothesis is true, should economic freedom or security strategies dictate US policy?