Sam Tanenhaus's recent cover story in the The New Republic provides fascinating — and ironic — historical perspective. Back in 1968, when Kevin Phillips was formulating the infamous "Southern strategy" that secured Nixon the White House, he was willing to dispense with big city votes altogether. "Who needs Manhattan when we can get the electoral votes of eleven Southern states?" Phillips asked. "Put those together with the Farm Belt and the Rocky Mountains, and we don't need the big cities. We don't even want them."

The old GOP strategy, Tanenhaus observes,"was built for a different time, and a different America." Of the 15 largest U.S. cities, 11 went for Obama this past November. Not just the big, traditionally blue cities of the Northeast, Midwest, and West Coast, but a number of fast-growing Sun Belt cities as well.

Just as cities and metros provide the economic engine of the U.S. economy — generating 85 percent of economic output — they have also become a singular political force.

But what are the factors that are shaping their votes and redefining U.S. politics? To what degree — and why — might this "metro-ification" of American politics work in favor the Democrats and against the GOP?

Election returns are not collated by metro, but county-level results are available. My Martin Prosperity Institute colleague Zara Matheson matched the county-level data provided by The Guardian to the metros made up by those counties, and then mapped the shares of Obama versus Romney vote for every metro in the lower 48 states.

Obama took the coastal metros in New England, the Northeast, and across much of the Eastern seaboard, from Portland, Maine and Boston to Washington, D.C., and even as far south as Charlotte and Atlanta (which Obama took by small margins), and Orlando as well as Miami. On the West Coast, Obama won the big metros, from Seattle and Portland down to San Francisco and Los Angeles. The President took many of the bigger metros of the Great Lakes region — Chicago, Minneapolis-St. Paul, Detroit, Cleveland, Buffalo, and Rochester. The President took 56 percent of the vote in Las Vegas, 55 percent in Denver, and 54 percent in Albuquerque. He also did well in several Texas metros, winning more than three-quarters of the votes in heavily Hispanic Laredo, 70 percent of the votes cast in McAllen, and more than two thirds of the votes cast in El Paso and Brownsville.

Romney, on the other hand, dominated smaller and medium-size metros in the Sun Belt. He won Provo, Utah, with 88 percent of the vote, and took eight out of 10 voters in Amarillo, Texas. In fact, four of the 10 metros that gave Romney his biggest margins were in Utah: Logan (84.3 percent), St. George (82.6 percent), and Ogden (77.2 percent) are the others. Three of Romney's top-10 metros were in Texas: Midland (80 percent), Abilene (76.9 percent), and Wichita Falls (75 percent). Romney carried roughly 60 percent of the vote in Oklahoma City; Birmingham, Alabama; and Jacksonville, Florida (which he won by an even bigger margin than Salt Lake City). He carried Dallas, Houston, and Phoenix, and Nashville with 55 or so percent of the vote.

Romney was also competitive in a number of older industrial metros. He took the old industrial regions of Wheeling (57 percent) and Weirton, West Virginia (54 percent), and Johnstown, Pennsylvania (58 percent), as well as Dayton (53.5 percent) and Cincinnati, Ohio (57.7 percent) by considerable margins. He even eked out victories in the once-blue strongholds of greater Milwaukee (51.7 percent) and Pittsburgh (with 50.03 percent vs. 48.8 percent for Obama). The once solidly-Democratic industrial belt is now mixed.

All told, Romney won more metros than Obama did, 214 to 150. But the President won the biggest, taking more than 60 percent of the vote in New York, L.A., and Chicago. Metros with more than one million people went for Obama by a margin of 53.4 percent to 45 percent for Romney. Metros with fewer than 250,000 people went decisively for Romney, by a margin of 55.6 percent to 42.6 percent. Metros between 500,000 and one million people were close, tilting 49.7 percent Romney to 48.6 percent for Obama; metros with between 250,000 and 500,000 people went for Romney as well, 50.7 to 47.6 percent. The average Obama metro is home to more than one million people, more that double the size (413,000 people) of the average Romney metro.

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But what is it specifically about big metros that made them trend blue?

To get a better sense of this, my MPI colleague Charlotta Mellander ran basic correlations between the share of metro votes for Obama and Romney and metro characteristics like education, income, occupation and socio-economic class, population density, and commuting patterns. As usual, I point out that correlation points to associations between variables only, not causation.

Density played a key role in the metro vote. (To capture it we use a measure we of population-based density, which accounts for the concentration of people in metro). The average Obama metro was more than twice as dense as the average Romney metro, 412 versus 193 people per square mile. With a correlation of .50, density was an even bigger factor than population (where the correlation is .34). The reverse pattern holds for the share of Romney votes; the negative correlation for density (-.51) was significantly higher than that for population (-.33).

The concentration and clustering of people is a key factor in innovation and economic growth; it also seems to turn metros blue. Shortly after the election, Maryland-based entrepreneur Dave Troy identified the inflection point when counties turn from red to blue as roughly 800 people per square mile. "[B]elow 800 people per square mile," he wrote on his website, "there is a 66 percent chance that you voted Republican. Above 800 people per square mile, there is a 66% chance that you voted Democrat. A 66 percent preference is a clear, dominant majority."

Education was another big factor in the metro vote. Economists have long noted how the clustering of highly-skilled, highly educated people powers the economic growth of cities. And as with density, the higher the level of education for a metro, the more likely it is to be blue. This becomes clear when we break metros into four groups, or quartiles, by their share of college grads. Obama took the top quartile — those with the largest shares of college grads — by a ten percent margin, 54.2 to 44 percent (the other three quartiles went for Romney).

The chart below plots the relationship between a metro's share of college grads and its share of Obama votes. The line slopes steeply upward showing how the share of Obama votes increase alongside metro density. The share of college grads in a metro is positively correlated with the share of Obama votes (.42) and negatively with the share of Romney votes (-.44).

The kind of work voters do — economic class — also helped shape their partisan voting patterns in metros. Creative class metros — those with high concentrations of workers in science and technology; business and management; healthcare, education, and arts, culture and entertainment — voted for Obama; working class metros went for Romney. Obama's edge in metros with the top quartile of creative class workers was 14 points, 56 percent to 42 percent. Romney, on the other hand, won 80 percent of the metros in the top quartile for the working class.

The chart above shows the relationship between the share of the creative class and the share of Obama votes across metro areas. The line slopes steeply upward, indicating a considerable positive relationship. The share of creative class workers is positively correlated with the share of Obama votes (.40) and negatively with the share of Romney votes (-.41).

Romney may have positioned himself as the candidate of high-tech industry, but high-tech metros were more likely to fall in Obama's camp. The President won more than two-thirds of the vote in Silicon Valley (the San Jose metro) and Boulder, which Business Week named the top metro for start-ups; more than three-quarters of the vote in San Francisco and Boston; and more than 60 percent in Seattle, home to Microsoft and Amazon. The concentration of high-tech industry across metros is positively associated with Obama votes (.35) and negatively with Romney votes (-.35).

Not just the kind of work we do, but the way we get to work is associated with metro voting patterns. Across metros, the share of Obama votes is positively associated with the share of commuters who take public transit (.44), bike (.30), and walk (.33) to work (the correlations are substantially higher when we consider large metros alone). Metros where workers drive to work alone went for Romney (with a correlation of .37). Of course, transit is much more available in denser metros, and people are more likely to live closer to where they work as well, so this finding also likely reflects the role of density.

For all of Obama's union endorsements, metros with larger shares of blue-collar workers in manufacturing, transportation, and construction voted for Romney (with a correlation of .46) and against Obama (-.45). The chart above graphically shows this, plotting the relationship between a metro's share of blue collar workers and its Obama vote. The line slopes steeply downward, showing the the negative relationship between the percentage of blue-collar workers and the share of Obama votes. The higher the share of working class votes in the metro, the less likely it was to vote for Obama.

These results are in line with a detailed analysis of county voting patterns from 1988 through 2008 that I conducted with my National Journal colleague Ronald Brownstein last September. Over the past 25 years, counties with higher creative class shares have trended more and more Democratic. In 1988, the Democratic margin in counties with the highest creative class concentrations was a substantial 6.1 percent; by 2008 it had ballooned to an overwhelming 23.7 percent. As Brownstein put it, a class inversion — in which college educated white professionals were increasingly voting Democratic — had "reshaped the electoral landscape," creating a powerful new source of class advantage for the President. A few weeks ago, Brownstein also noted that "so many of the blue-collar and older whites who formerly anchored the conservative end of the Democratic base" have virtually "abandoned" Obama.

Republicans may still be the party of the rich, but most of the country's more-affluent metros lined up squarely in the Obama camp. The correlation between the average wages and salaries of metros and the share of Obama votes is positive (.50) and it is negative for Romney votes (-.51). This makes sense too, as larger metros have greater concentrations of knowledge-based talent and industries and are wealthier to begin with. (The associations we find are even more substantial for metros with more than one million people, with the correlations increasing to .71 for Obama and -.72 for Romney.) This follows the "Red State, Blue State, Rich State, Poor State" pattern identified by Andrew Gelman of Columbia University, who infamously found that while rich voters continue to trend Republican, rich states trend Democratic.

Interestingly — and contrary to the much-stated view that Obama purchased the election with welfare, food stamps, and other entitlements (in Rush Limbaugh's words, "It's just very difficult to beat Santa Claus"), our analysis turned up no statistically significant association between Obama votes and the metro poverty rate and only a very small one for income inequality across metros.

Then there's the widespread perception that blacks and Hispanics gave Obama his decisive edge. While Obama clearly carried black and Hispanic voters, race appears to have played less of a role at the metro level. Surprisingly, Mellander found no statistically significant association between a metro's share of black residents and the share of Obama votes and only a weak association between a metro's share of Hispanic residents and Obama's vote share (.17).

Diversity did play a role in the metro election, but across different dimensions than race. There is a considerably stronger positive correlation between a metro's foreign-born share and Obama votes (.38), and a negative correlation to Romney votes (-.38) — which is precisely why many Republicans are re-thinking the political wisdom of their anti-immigration stance.

Obama's shift on gay marriage in May of 2012 might well have paid dividends in November. There is a positive correlation a metro's Gay and Lesbian Index and its share of Obama votes (.49), and a negative one between it (-.50) and the share of Romney votes (see the chart above).

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America's political divide is an outgrowth of its increasingly divided economic landscape. The very same forces of talent-clustering and knowledge industry concentration that shape the divergent economic fortunes of our cities and regions, increasingly shape our politics. Affluent, high-tech, creative class metros — big ones like New York and L.A., high-tech ones like San Jose, Seattle, Boston, and San Francisco, and smaller college towns like Boulder, Madison, and Ann Arbor — are mostly blue. Less advantaged, less skilled metros in the Sun Belt and even in the Midwest are increasingly red.

America is divided between cities of knowledge and skill and the rest. The residents of these knowledge cities not only do better economically, they are better-traveled, better-connected to the global economy, and more open to diversity. Perhaps because the work of the knowledge-based metros centers turns on knowledge, creativity, and abstract thinking, their residents tend to be more open to the notion that government can help improve the economy, better the environment, provide essential services (like healthcare), and protect the fundamental rights of disadvantaged or discriminated-against groups. (This is in line with Ronald Inglehart's detailed research on the shift from interest-serving "materialist" politics to a more "post-materialist politics" — which puts more emphasis on individual self-expression, shared rights, and public goods — in knowledge-based economies).

Those who live outside these places see knowledge-based centers as elitist and coddled by government. They are well aware of the growing gap between the metro haves and have-nots, and know they are losing ground. They'd like to somehow stop the forces of change that are leaving them behind and bring back the good old days when they, and their more traditional vision of, America was on top.

This divide is as economic and geographic as it is partisan. America's polarized politics is a product of its deeply-etched geography of class.