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.
It's pitiful that this is the best boogeyman the right can come up with in 2020 and it's extra pitiful that - like everything else they project - it's just them telling on themselves.