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.
Portland itself outlawed black residents in the 1840s and that law stood for many decades. It's only very recently that Portland has developed the reputation for having a liberal populace; as recently as the 1990s it was essentially the white supremacy capital of the west coast.