Let us say that a foreign government (the Duchy of Grand Fenwick) wants to question a US citizen about something. At the time of the request the citizen in question is peaceably minding his own business at his home in Topeka, Kansas. The Duchy's government has not promised to return the citizen after their questioning is complete.
Let us also say that at the time of the request, the US administration would like very much for the citizen to leave the US and not come back and thus is more than happy to honor this request.
If the citizen is not willing to be questioned or to leave the country, what conditions must the US government meet in order to lawfully arrest the fellow and hand him over to the Fenwickian state?