What makes someone most likely to be a Bernie Bro

[All Along The Watchtower]

Being male, for one (and presumably cis male though I'm not sure if that's been established).

Beyond that, hating both parties - can't imagine why! -  but also hating Donald J. Trump and recognizing that third parties are a waste of time because of the US electoral system (and because most actual third parties are bad jokes).

Oh, and thinking capitalism at least in its current form is catastrophically bad.

[All Along The Watchtower]

The beliefs track to young people falling out of the middle class. Participation in rose Twitter (or online political communities generally, us too) suggests feelings of isolation and a resulting drive to find community in the virtual world.

Also this.