They mostly don’t think he’ll help, or they’re not overly confident. They are though, confident that the “establishment” options would be worse, and they loathe the idea of equality of outcomes under socialism, and that’s enough for them.
The other factor is that the more desperate you get, the more willing you are to take that outside shot at changing things for the better. The more poor rural folks and the white working class feel backed into a corner, the less they feel dedicated to stability. It’s a feeling of “well it can’t get any worse.”