When we think of voting patterns and political trends, we usually think in terms of interest groups, and that's because the political parties serve interest groups primarily. Politics to us is a contest between well-organized clubs who stand to gain or lose financially based on the outcome of legislation.
In general, elections come down to contests between two groups. The first consists of public sector bureaucrats, unions, the elderly who are protecting their government checks, minority groups who cling to special privileges, the winners in the welfare-state lottery, and marginalized oddballs of all sorts who resent cultural impositions by bourgeois America. That group is also known as the Democrats.
They are not all bad because they tend to fight against policies that do not benefit them, such as those policies that help the other group.
And that other group consists of large corporations who seek mercantilists privileges, the commercial class of small and medium-sized merchants who rightly want fewer impositions from government, the Wall Street elite who favor a form of free enterprise that is compromised by loose credit and socialized protections against loss, middle-class producers and consumers who demand rising portfolios through any means possible, and the religious bourgeoisie who are always up for a good war against evil (drugs, moral deviancy, Islam, or whatever). That group is also known as the Republicans.
Yes, this is an oversimplification, but not as much as it might first appear.