Antifa was founded in Germany - therefore an international terrorist group so yes he can declare.
Yes, the 1930s group was there.
There is not an organization here. It isn’t like BLM. They are a bunch of people being goaded on by a bunch of bad rich actors who have done a great job of not getting pinned down as part of some official organization.
Soros uses a lot of people and small groups, but he clearly has set up a way that he is not a “leader” of some movement.
It’s the same reason the KKK isn’t a “terrorist organization”, because there is no “KKK” anymore, just a bunch of small organizations who call themselves KKK.