I really do not think they are not capable. They are better of stealing a nuke from Iran,Russia,China or North Korea where is much easier with no safeguards like we have.
Disassembly? Don’t know... But I can guarantee that they know how to use Google and darn sure can find out about the B-61. If they’re that ignorant, then give them bombs and grenades and let them practice and kill themselves.
Therefore we only need to be not quite so careless, not quite so neglectful, and not quite so slovenly.
OTOH, some opponents might find if more satisfying to use our own technology against us.
A society that will never be capable of making a passenger jet just might produce a score of individuals willing to give their lives to use a few to just to make a point (and get a free admission ticket to a whorehouse-in-the-sky)