Are you familiar with George Lakoff’s view of the difference between conservative values and liberal values (e.g. Moral Politics). Conservatives are drawn to a stern parent, usually a father-figure, as their leader (values of selfishness, self-protection); liberals seek out nourishing mother-figures (values of generosity, sacrifice for others). Mother and father figures can be men or women — Maggie Thatcher was a father figure, e.g.

Lakoff’s explanation fits your three categories of economics, culture, and incumbency. In theory, an economic downturn should work against Trump, but it may energize conservatives, who may fear that Sanders will give away the scraps they’ve hoarded up.