One of the most interesting recent developments in American voting behavior is the moderate attenuation of an extremely robust relationship between income and party identification. Historically, the more money you made the more likely you were to vote Republican. It was as simple as that.

In 1996, for example, Bill Clinton won 59 percent of the vote of those who made less than $15,000 a year, 53 percent of those who made between $15,000 and $30,000, 48 percent of those between $30,000 and $50,000, 47 percent of those between $50,000 and $75,000, 44 percent of all those between $75,000 and $100,000, and 38 percent of those who made over $100,000. In 2000, George W. Bush’s share of the vote in the same categories was 38 percent, 42 percent, 48 percent, 51 percent, 52 percent, and 55 percent.

Things then seemed to change. The 2008 exit pollsters used eight income categories in their data collection. Barack Obama won five of them; the bottom three (everyone under $50,000), but also the fifth from bottom ($75,000 to $100,000) and the top category — or those who made in excess of $200,000 a year.

Social and cultural politics most frequently are offered as an explanation. The argument is that many wealthier Americans are pro-choice and support gay rights, while many blue-collar workers are religious conservatives. Race and policies like affirmative action and school busing also cut across economic divides. As battles over issues like these naturally capture headlines, they increasingly shape voting decisions.

I believe there is another reason why upper-income Americans increasingly have become a bit more Democratic.

Forty years ago, there seemed to be few differences between business owners and professionals. They moved in the same social circles and shared the same pragmatic but intrinsically conservative values. As the country and Republican Party have changed, however, the two groups have been pulled apart.

Many professionals, like doctors, lawyers, scientists, and professors, oppose central tenets of the GOP’s current philosophy. It is generally they who are voting for Democrats.

Because they provide services, professionals must be close to people, leading many to live in urban areas. They have a greater appreciation for public facilities like mass transit, parks, and the arts and they consume them. They might not tolerate the crime, crowdedness, and inconveniences of city life — there are always, after all, private schools for their kids and clubs for their recreation. But they understand it and its messy diversity. The various places of worship, the eclectic restaurants, and the cultural opportunities add to the richness of life.

Professionals are advocates for others. Although this thinking emanates from hundreds of years of tradition and culture, it is not solely an act of altruism. Doctors need patients, lawyers need clients, and professors need students to make a living. But it does compel them to think in a more communal, and less individualistic, way. In other words, their work encourages them to think less like Republicans, especially Republicans in the 2000s.

Professionals also like a dollop of government. Licensing requirements keep competitors out of their fields and protect the investments of time and money they have made in their post-graduate educations. Scientists rely heavily on federal grants to do their research and many individuals come into doctors’ practices and lecture halls on the public’s dime.

Business owners and managers, by contrast, are less concentrated. Urban living is costly, so many move away from large towns. Many of the communities they live in are homogenous and often free of the kind of social problems government tries to solve. They dislike government regulation because it often harms their economic interests — although, like anyone else, most are perfectly willing to accept subsidies and tax breaks. They serve customers but they enter the relationship focused entirely on their profits.

Business is, of course, not monolithic. Over the past couple of decades small business, largely through its trade association the National Federation of Independent Business, has emerged as one of the most influential constituencies of the Republican Party.

NFIB detests the kind of regulation large corporations tolerate. Increases in minimum wage and environmental standards advantage big businesses because they can absorb costs that might kill off smaller competitors. New health care insurance mandates hardly will affect multinationals but may cripple many small businesses. NFIB cares less about liberal immigration laws because members tend not to employ many foreign workers.

In other words, this business-professional split is a little more complex than first appears. Big business types, the very rich, can be won over to the Democrats’ policies. They are the genuine battleground for the parties, not least because they have deep pockets. CJ

Andy Taylor is a professor of political science in the School of Public and International Affairs at N.C. State University.