That is a very misleading and erroneous method of approach to this subject.
We do track all ships coming and going from the USA. Only specific ships that are from specific areas or have deviated from predetermined schedules or have been flagged for one reason or another are inspected.
Much of the cargo that comes in is coming from known sources and thus are given more latitude.
I pack ( twenty foot Equivalent Units) TEUs in Malaysia, I make 10 dollars a day and a nice korean man offers me 1000 dollars to add ten boxes to the TEU. They look just like all the other boxes and I just half to look the other way.
So even if the TEU comes from a port we know with good bills of lading guess what, contraband is in the 95 % we don't look at.
Have a nice day