threats against leaders

I know that threatening to kill the president is a huge crime, but what about an American threatening to kill the leader of another country, such as a member of England’s royal family or some prime minister? Would that person be extradited from the US to the country in question?

Well, we only extradite people upon request of another country, so England would first have to charge them and requist extradition.

And why would they bother to do that (and pay for it) if the person making the threats is thousands of miles away?

They’d be smarter to just leave the threatener far away, and maybe add their name to a customs list of ‘people not allowed into England’.