There are two further issues that the United States must deal with in defining the threat: the possible nature of the attackers and the possible means of attack. In broad terms, the United States has done a good job of identifying potential attackers and the means that they might use. It does, however, need to improve its threat and risk assessments in terms of the ways in which it analyzes attackers and determines if they might use WMD.
The United States is inherently vulnerable to covert foreign attack. America is an extraordinarily open society dependent on massive volumes of foreign trade and immigration. It has nearly one hundred thousand miles of shoreline and six thousand miles of borders. Some 475 million people and 142 million trucks and vehicles cross the border every year. There are 21.4 million major container-sized cargo shipments a year, plus countless break bulk and individual shipments. The legal trade across the U.S. borders arrives daily at 3,700 terminals in 301 ports of entry. 1
Customs searches a tiny percentage of legal shipments into the United States, and much of the processing is pro forma. Most air forwarding enters the United States without any inspection. Containers can enter the duty-free areas of U.S. ports and remain there for thirty days before a declaration is required. Roughly eight million containers enter the United States each year, and one container takes an average of five inspectors three hours to