[paduc]

I think that you are correct. I was looking for this in the comments.

At that period in history, the French kingdom (catholic) was at war with the Spanish kingdom (also catholic) and Italian kingdoms/duchies. A pope had immense political power because of the fervor of the people. If the pope excommunicated a king, he would lose a lot of power in his kingdom and all catholic countries would have a good reason to declare war. Hence, the strategical relocation of "a" pope in the city of Avignon, under French "protection".

I believe the threat is to "protect" a new pope in the US. Whether catholic (maybe other christian denominations) Americans would support it...