“Authorities check a fraction of the cargo containers moving through our ports, so it is highly likely that N Korea could move nuke components into the USA. “
Wrong conclusion, and ignorant of our nuclear detection systems, not to mention ignorant of nuclear materials, which can track any and all nuclear materials. We don’t need to physically inspect each container to know if any particular container has nuclear materials in it.
I'm glad you have so much faith in our authorities to keep us safe. They can't track all nuclear materials. They say they can. Just like every test of TSA airport security at preventing test smuggling of weapons has failed, dramatically.
https://cisac.fsi.stanford.edu/sites/default/files/Detecting_Nuclear_Material_in_Shipping_Containers.pdf
"... from a systems perspective, the permissible failure rate for commercial inspection systems falls short of a tolerable threshold for security—some losses due to crime are accepted as part of “the cost of doing business.”
That's from measures adopted voluntarily by commercial operators to assist authorities.
"No single technology can detect illicit nuclear weapons and materials with 100 percent reliability."
All it takes is a single failure in detection. Currently, all detection procedures are experimental and take cooperation with commercial operators. I'm glad you sleep well at night thinking our government is doing a perfect job. I'm not so sure.