By The Economist
http://www.economist.com/node/17525707?story_id=17525707

AMERICA is getting used to political upheaval. Barack Obama’s election was, to many voters, a moment of transformation. His first two years, many others lamented, brought a dangerous expansion of government; now the right has arisen again. The new Congress will be more polarised than at any time since Reconstruction, reckon some political scientists. But these swings, however large and consequential, are arguably only symptoms.

If people feel as if the country is changing quickly, that’s because it is. The first set of numbers from the 2010 decennial census will be published in December. They will, sadly, be less interesting than in previous decades, as the census form has been radically shortened this time. But plenty of other data get collected by the Census Bureau every year, and our trawl of what has been gathered over the past decade already reveals some seismic shifts. Baby boomers are retiring in large numbers; the young are more racially diverse than ever. Hispanic immigrants are transforming communities, bringing both promise and tension. The first decade of the 21st century was not kind to America’s middle class—real median household income was 7% lower in 2009 than it was in 2000. The gap between rich and poor widened. And the young are doing relatively badly in education.

All these trends are enough to shake a nation. Just as important, however, is that they are playing out very differently from one part of the country to another. Of course, some variation is inevitable; but as the fault lines that criss-cross the country widen, finding political consensus becomes ever more difficult.

In one important respect America has a sunny demographic outlook. Its elderly may be growing in number but, to the envy of other developed countries, America also has a burgeoning young population. However the distribution of old and young makes this picture more complex.

For decades Americans have followed the sun westward. This shift continued from 2000 to 2007, when the gathering recession all but stopped migration. However the populations of the north-east and Midwest have not just shrunk (which means that the census will require them to give up congressional seats) but become greyer. Young families leave, often to look for economic opportunity or an affordable home (Michael Bloomberg, New York’s mayor, calls his town a “luxury city”).

Between 2000 and 2009 Maine surpassed Florida as having the highest concentration of those 50 and older, according to the Census Bureau’s American Community Survey. Of the 20 oldest states in 2009, 14 were in the north-east and Midwest. The sunbelt, in contrast, was home to eight of the ten states with the highest concentration of youth. Austin’s number of married couples with children rose by 24%; Youngstown’s shrank by the same.

America’s young and old are differentiated not just by region but by race. Hispanic immigrants in particular are helping to swell the ranks of the young. The decade saw America’s foreign-born population grow by 24%, or about 7.4m. In 2009 Hispanics comprised 21% of those younger than 25; those 65 and older were 80% white and only 7% Hispanic.

But this divide—what William Frey of the Brookings Institution in Washington, DC, calls “the cultural generation gap”—is very much wider in some states and cities. In Arizona, for example, 83% of the elderly are white and 42% of those under 25 are Hispanic. This can lead to divergent priorities, such as the reluctance of the old to pay for education, or even a political eruption. This year Arizona’s anti-immigration ordinance sparked protests far beyond the state’s borders and a lawsuit from the federal government.

Such conflict may well be replicated as other places welcome (or fail to) new residents. Immigrants are increasingly dispersed, settling in areas unused to outsiders. South Carolina’s Hispanic population expanded by 116% between 2000 and 2009. South Dakota, Tennessee and Alabama also saw big jumps.

In the long term, these immigrants or their children may become local economic stars. In the short term, tension is mounting. Mr Frey found that many of the new magnet states attract immigrants unlikely to speak English or to have completed school. Voters in such communities may view immigration rather differently than do those in San Francisco or Pittsburgh, hubs for skilled, foreign-born workers.

There is also a range of subtler shifts. In his 2008 book “The Big Sort”, Bill Bishop argues that communities are differentiated not just by demography but by the way people live. In the 1960s and 1970s communities on the whole grew ever more alike. But since the 1980s they have diverged on a range of indicators, from the age at which women have children to the age at which residents die. The most powerful “sort”, however, may be the slow concentration of educated workers.

America as a whole is becoming better educated. In 2000 24% of those 25 and older had a bachelors degree or more. By 2009 28% did. But this rise is not uniform across ethnic groups—blacks and Hispanics are lagging—or throughout the country. In the 1970s America’s college graduates were distributed relatively equally among cities. Since then, however, the skill-level of metropolitan areas has diverged. Brookings ranks the 100 biggest metropolitan areas by rate of educational attainment. The gap between the most and least educated cities was 26 in points in 1990. By 2009 it had widened to 34 points.

These trends, if they continue, will surely affect regional prosperity. From 1999 to 2009 median household income rose in only five states, and in four of these the gains were driven by soaring commodity prices. The biggest drops in income were all in states that depend on low-skill industries: Michigan, Indiana and Ohio.

During the recession, education was workers’ best shield. Of the 20 best-educated metropolitan areas, only four saw their employment rate drop further than the national average, according to Brookings’s Alan Berube. The worst-hit areas were those dependent on construction and manufacturing. It was there, too, that women began to support their families in higher numbers—3.4% of families had an unemployed husband and a working wife in 2009; Florida, Nevada, Michigan and Ohio had shares well above the average.

E pluribus unum?

All these conflicting interests are helping to polarise further America’s politics. In the 1976 election, explains Mr Bishop, 26% of voters lived in counties where one party won by 20 points or more. In 2008 a whopping 48% of voters did so. Strikingly, less than 400 of America’s 3,141 counties switched parties at the 2008 election. Politicians, like marketers, have become adept at identifying likely customers. “Bringing out the base” is the key to winning.

As a result of this polarisation, satisfying a range of constituents is becoming harder. The federal stimulus revealed this well. The bail-out gratified some Wall Street bankers. Aid to state governments mostly helped workers in capital cities. But voters in places with battered housing markets got little benefit from either. James Gimpel, a political scientist at the University of Maryland, notes that areas with high rates of foreclosure, such as suburban Atlanta, were hotbeds of tea-party activism.

The best hope for a return to moderation may lie in America’s suburbs. Once blandly homogenous, suburbs are now home to a majority of America’s Asian, black and Hispanic populations. They are increasingly filled not just with the rich and middle class but the poor. It is little wonder that the closest political battles are often waged in suburbia. For now, however, more polarisation seems likely. This year many moderate Democrats either retired or were sacked. “There is much too much partisanship and not enough progress,” Evan Bayh lamented as he announced his retirement from the Senate.

So from January Congress will include a higher proportion of lefty Democrats and a new crop of conservative Republicans. Keith Poole, a political scientist from the University of California, San Diego, thinks the 112th Congress will be the most divided since the end of the civil war.

With the federal government deadlocked, bold measures may be confined to state and local governments. Already, Mr Bishop points out, states find it easier to pass controversial initiatives than the federal legislature does, whether that be allowing gay unions in the north-east or banning embryonic stem-cell research in South Dakota.

In some respects, decentralised policies make sense—local and state politicians are better suited to tackle divergent needs. But America has big national problems. Increasing divergence will not make agreeing on how to deal with them any easier.