I think the good ol’ Alt-Right Playbook can shed some light on that one.

I linked to the specific part of the video that explains the particular point I want to make, but I recommend watching from the beginning anyway. Also, the extra-short TL;DR is basically that the Democratic party is structurally predisposed to continually give the benefit of the doubt and assume good faith, even when it is not only blatantly undeserved but also being actively exploited by their opponents.