I have often wondered about this myself. This article goes a long way towards making sense of the issue. Possibly the most cogent point in the article comes from Thomas Frank.
"Thomas Frank says that whatever disadvantaged Americans think they are voting for, they get something quite different:
You vote to strike a blow against elitism and you receive a social order in which wealth is more concentrated than ever before in our life times, workers have been stripped of power, and CEOs are rewarded in a manner that is beyond imagining.
"It's like a French Revolution in reverse in which the workers come pouring down the street screaming more power to the aristocracy."
I have to disagree with the author's comment that "This is a culture war but it is not simply being driven by differences over abortion, or religion, or patriotism." Somehow the party of big business has co-opted moral and patriotic authority as their domain, and branded the party of the working class and poor as morally bankrupt. How did they manage that? Could it be as simple as having more advertising dollars?