Universal scanning challenges detailed by DHS.

Stewart Baker, assistant secretary of Homeland Security for policy, told a congressional committee recently that he is "daunted by the prospect of 100 percent scanning in every port" and "there are many challenges." He also said the department will pursue that goal "aggressively."

Among the challenges in fulfilling the whimsical recommendations of the 9/11 Commission that Congress turned into PL 110-53 are the following:

* Installing equipment has required reconfiguring ports' layouts, which vary greatly.

* The concrete used at each port can create difficulties when it emits natural radiation that throws off sensors. …