Not sure if you are being sarcastic, but I actually said this same thing to my wife earlier. The difference is, in my scenario it is the North Koreans. They have the weapon...what they need is a delivery system. Do people really not believe the Iranians and North Koreans are capable of concocting stuff like this?
All they have to do is get the plane to Hawaii, and it'll make what Japan did at Pearl Harbor look like childs play.
In fact, they don't even have to land...an air burst will do just fine.
To get there, they could release the plane, pilots and crew, and give them instructions to fly to Hawaii seeking asylum/defection the whole way. They could keep the passengers as leverage. The crew wouldn't have any idea there is a nuke on board.
When the Navy scrambles fighters to intercept, they wouldn't be able to detect a nuclear signature...and Obama would have to make an executive decision. Shoot it down or let it land.
And then what? If North Korea did this successfully and claimed responsibility, what exactly would Obama do? Attack North Korea? To what end? All those civilians are interlaced throughout the entire country. There is no separation between their industrial military complex and the people who are victims of a communist regime. Seems like an easy decision, but is it? What if North Korea and Iran both claimed responsibility?
If we didn't react, then Russia and China would be licking their chops...finally seeing the US as the paper tiger it has become.
Anyway, they'll probably find the plane/debris in within the next few days, and this will all be over. But man, the "what if" scenario of a stowawayed nuke is definitely realistic...and scary.