It wouldn't happen. They'd arrest him.

Or, to put it another way - it would happen; it just wouldn't be called assassination, because it would be done using standard police procedure, and because other people would get killed. It would be like the standoffs with MOVE, or David Koresh's organization in Waco, or Ruby Ridge.

The word assassination is wrong for all these cases. These kinds of "assassination" are just the logical result of law enforcement. If you're enforcing the law, and you have police and courts and so on; and someone refuses to play along, eventually you have to use force. I don't see that the person being outside or inside America makes a big moral difference, when their actions are having effect inside America. A diplomatic difference, but not a moral difference.

I also think it's funny for people to have moral arguments in a forum where you get labeled an idiot if you admit you believe there are such things as morals.

Perhaps we should be grateful that technology hasn't advanced to the point where we can take these people out non-violently, because then we'd do it a lot more, for more trivial reasons.