Note how the Trump supporter is wearing a swastika armband (and the skinhead making a Nazi salute and Hitler as well.) Garrison is past trying to say that Trump isn't racist, now he is fully admitting that Trump and his supporters are white supremacists.
That, or since these are ghosts specifically haunting Sanders, they would appear as Sanders (ie "the left") might envision them, that is, as white supremacists, neo-Nazis, and such, which is just further proof of the delusion that Garrison is saying they're under.