thatcrowCould a nuclear bomb be delivered and detonated via a truck or boat?
Easily. That is one reason why ports and other national entry points have systems in place to detect that. Of course there is nothing to stop a bad actor from reaching the border or coast with a weapon and setting it off.
Yup, as a foreign national, I had to jump through a myriad of hoops to get a TWIC which enables to enter and exit US ports freely without someone escorting me around. Fun fact: A TWIC allows even foreigners to register as a known traveler, allowing me to skip a lot of the hazzle when flying in the US.