I’ve thought for years that if an enemy wanted to nuke us, a shipping container would be the ideal delivery system. I don’t know how closely they are checked, or how they could be insulated against detection, but a huge weapon could be put in one. There are many thousands of them on ships around the world at any given time.
Thousands on a container ship. Put it on the bottom and shield it with more containers full of lead or another suitable shielding material and just be patient. Track the ship over the internet and call the special cell phone number when it ties up to be unloaded.
https://www.marinetraffic.com/en/ais/home/centerx:-74.140/centery:40.671/zoom:14
Even not very powerful it would vaporize the ship and probly the terminal and make a big radioactive hole in New Jersey (where it belongs) and cause mass hysteria. Maybe a little more $$ than 9-11 but they have just about everything they need to pull it off already in place.