Then, you are deluded and historically illiterate.
Democrats have been physically attacking and terrorizing their opponents since Andy "Ol' Crook" Jackson attack dogs were beating, murdering and committing arson against people who did not want to bow down and worship the crazy bitter old coot.
Please put down the sugar tits they fed you in school and start reading the actual news articles of the time.
This author is a head in the sand fool or incredibly naive. Besides not thinking the left has not been in American politics, whole article seems to be over intellectualizing leftist violence, which is a large part of the problem in the first place.