A recent paper from the Russell Sage Foundation reports that income-based residential segregation in America has risen sharply over the past 40 years; in 1970 about 65 percent of families lived in middle-income neighborhoods but only 44 percent do so today. The rest now live in neighborhoods that are distinctly either rich or poor, with affluent Americans being especially likely to be surrounded by their income peers. These findings parallel estimates we have been making, from different data, since 2005. In a generation, the spatial polarization of incomes has become an American fact of life.

Does this fact have political implications? We believe it may. Indeed, there seems to be a party that’s benefiting from increasing residential segregation by income – and, oddly enough, it’s the Democrats.

The Columbia political scientist Andrew Gelman has noted an apparent paradox: in presidential elections rich people tend to vote Republican, but rich states tend to vote Democratic. This can happen because the income-voting relationship differs from state to state. Thus in wealthy but arch-blue Connecticut the relationship is much weaker than in non-wealthy and arch-red Mississippi – a fact that prompted Gelman to ask, in the title to one article, “What’s the Matter with Connecticut?”

But why should the wealthy in (say) Connecticut (or California) tend to be Democrats while those in Mississippi (or Texas) so rarely are? We suggest a possible explanation: It’s not where the wealth is that matters — it’s how insulated it is from where it isn’t.

While income inequality, measured between persons or households, is higher in Mississippi than in Connecticut, spatial segregation is greater in Connecticut. That is, in Mississippi, rich and poor tend to live quite near each other, inside the same towns, counties and school districts, while in Connecticut, which is a well-known mosaic of wealthy and working-class towns, they don’t. And that means that in local politics, at least, Connecticut’s rich and the poor are often not in direct political conflict. They don’t live in the same towns, sit on the same school boards, argue quite so much over zoning or local property taxes. So conflicts rooted in class (and also in race) tend to be muted. None of this makes it easier for the poor to be Republican. But it does make it a bit easier for the well-to-do to be Democrats; it weakens their class politics, at least at the national level.

If this explanation is about right, then spatially-segregated states should tend to vote Democratic in presidential elections, and spatially homogeneous ones should tend to be Republican. How well does this prediction hold up? Here are the results for 2000 and 2008.

In 2000, the ten most polarized states (by our measure, in order) were New York, Connecticut, California, Massachusetts, New Jersey, Washington, Maryland, Illinois, Virginia and Michigan. Of these only Virginia voted for George W. Bush. The ten least polarized states were South Dakota, North Dakota, Montana, West Virginia, Vermont, Iowa, Kentucky, Mississippi, Arkansas and Wyoming; of these only Vermont and Iowa voted for Al Gore.

By 2008, the map had changed a bit. Michigan had dropped back in the rankings, while Florida entered the top-ten. Barack Obama won each of the ten most polarized states. Meanwhile the ten least polarized states had added Nebraska while losing Wyoming. Of the 10 least polarized states in 2008, John McCain lost only Iowa and Vermont.

And what does the list foretell for 2012? Here are the least polarized states, as of 2010: South Dakota, North Dakota, Montana, West Virginia, Kentucky, Iowa, Vermont, Mississippi, Nebraska, Arkansas, Oklahoma, Wyoming, Louisiana, Idaho, Maine, Alabama and Alaska. Of that list, based on current polls the president will carry Vermont and Maine for sure, and maybe Iowa – though the polls have Iowa closer this year than four years ago. The rest are Mitt Romney’s, almost for sure.

As for the most polarized states, they are New York, Connecticut, Massachusetts, California, New Jersey, Maryland, Washington, Virginia, Pennsylvania, Illinois, Florida, Hawaii, Arizona, Minnesota and Delaware. Is there a sure Romney state in the lot? Well, Florida is a battleground, and Virginia remains close enough in some polls. And there’s Arizona. Arizona went for Bush and of course for McCain, but it is, according to some polls, “Barely Republican,” this year.

Is the relationship between spatial segregation and electoral outcomes a statistical fluke? It could be: we haven’t tested alternative models and maybe the relationship we observe has another underlying cause. But we think there’s something to it. The adage that familiarity breeds contempt has, it seems to us, the awful ring of truth.

And if this is true, then the strong movement toward an income-segregated America – a movement led especially by rich folk escaping from big-city schools and property taxes – could have an interesting side effect. Down the road, by easing the class conflicts of an increasingly unequal nation, it could produce final defeat for the national Republican Party in presidential elections. After all, the Electoral College is winner-take-all – and while the fifteen most geo-polarized states have 253 electoral votes, the seventeen least polarized states have only 86.

It seems that “not getting out much” could carry a heavy cost, and not just this year, for Republicans. Whether it will lead to a Democratic Party worthy of the name is another question.

James K. Galbraith’s new book, Inequality and Instability, is out now.