A Reverse Screening in the Transportation Security Agency's TSA Management Directive No. 100.4 is defined as a "Post-flight search of passengers, accessible property, and luggage conducted after the aircraft has reached its destination and before passengers or baggage are permitted to re-enter the sterile area of an airport.".
If a person were able to get on a plane and fly over here, and land--not having caused havoc on the plane--then any disruption at an international airport would cause a massive delay in a national and international air travel. If a terrorist were not planning on attacking the airport or hijacking the plane (most likely case) prior to arrival, transporting bad things into the country would be much easier via alternative methods.