Quoted:
Where is the Interstate/Foreign Commerce Nexus ? The Destructive Device never entered the United States...so, it never entered US Commerce. Therefore, the US doesn't have juristdiction.
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Items do not have to travel in interstate/foreign commerce to be regulated. They only have to [b]effect[/b] interstate/foreign commerce. The effect can be minimal and is looked at cumulatively. If I grow a potato in my backyard to feed to my family, I am engaging in interstate commerce because this will cause me to buy one less potato at the grocery store, which will cause one less potato to be imported to my state from Idaho. And thousands of other people are growing potatoes in their back yards. So Congress can regulate my growing a potato, even though that potato will never cross state lines or enter commerce. As Congress can regulate interstate/foreign commerce, it is "necessary and proper" to regulate those things which effect interstate/foreign commerce.
So what is outside interstate/foreign commerce? Basically nothing. The Supreme Court is carving out a few exceptions where there are issues of state sovereignty, but there is no reason to apply that doctrine to foreign sovereignty. I am not saying all of this is right, but it is the law as currently interpreted.
There may be other grounds for jurisdiction too.
I am not sure where that quote you cited came from. That is not part of the constitution; it might be part of the statute in question, which may limit the law's applicability, but it is not a restriction on Congress' power.