To guarantee your explosive gets on the plane you want, all you have to do is get an inside man.

Very few Americans would be willing to smuggle explosives, but plenty are willing to smuggle drugs. Make a few runs smuggling "drugs", then replace the "drugs" with an explosive payload.

Done deal, plane goes boom and you are a terrorist hero.

Of course the risk of smuggling would go way down if the TSA would only protect the luggage from molestation after the screening.