They (not Trump of course) had to walk it back when it turned out not to be true.
Is there some outside groups posing as others, possibly, but to blame a majority of problems on them is just BS.
I see a lot of mischaracterization of what is a category, not a group. From what I can tell antifa is anti-fascism, and somewhat characterized by people willing to take direct action.
"However, the followers must be convinced that they can overwhelm the enemies. Thus, by a continuous shifting of rhetorical focus, the enemies are at the same time too strong and too weak."