To send an atomic bomb to the US all Iran has to do is put it into a shipping crate. No miniaturization needed.
Those drones have 800km range. They can devastate both coastlines if they do it right and they might be undetectable until too late.
The Sum Of All Fears scenario?
Can the US credibly, efrectively screen with sensors/inspections everything brought in here to test for radiation or... lead-lined containers to mask radiation? How far away can we detect them?