The volume of containers entering our ports and transferred via rail/truck is enormous. There isn't sufficient resources to check them all. The asian countries use containers to move goods to the U.S. west coast, transport them to the east coast on railcars, then put them back on ships bound for Europe. It is the least expensive shipping path. It would be easy to smuggle just about anything into the country that way.
Attacking our seaports or rail lines is an attack on both the U.S. and on the supply lines to Europe from Asia.
Yes, you are correct.
I don't think that most have any idea of how many containers of goods are shipped into the U.S.
Or what we will need to survive, if the incoming containers are stopped.
Everything we eat, wear or use, has been in a container.