For those who believe that demography is destiny, there was no more jaw-dropping figure from the 2004 presidential election than this finding from the nation’s far-flung metropolitan frontier: George W. Bush carried 97 of the nation’s 100 fastest growing counties.

You could look out from say, Riverside County, Calif., or Henderson, Nev., to a vast, red-roof-tiled future. New century America was pulling young families and newly middle class immigrants to the far exurbs, creating a vibrant new habitat for the Republican Party.

Many of the cities, at least some of the more hollowed-out and aging urban cores, were written off as inconsequential. The new electoral game was in the places where farm fields were being plowed under for asphalt. In Karl Rove’s strategy for a “durable Republican majority,” as he called it, lasting at least a generation, the exurbs were a key component of his master plan.

After a monumental housing collapse, and eight years of less-predictable changes in where Americans live, that thinking has been thrown out.

Democrats made significant inroads in Rove’s demographic sanctuary, starting in the 2006 midterm election, which, it turns out, was the exurban population’s growth peak. In 2008, Barack Obama won 15 of the 100 fastest growing counties, including the three largest: Riverside County, Clark County (Las Vegas) and the Research Triangle of North Carolina, Wake County.

And now the population boom to the exurbs is over, at least for the moment, according to Census Bureau figures released earlier this month. An analysis of those numbers done by William H. Frey, a demographer at the Brookings Institution, found that growth in the cities, and densely-populated older suburbs, has eclipsed that of the exurbs since 2010.

For political strategists reading the fine print in county-by-county population shifts, Frey’s point is one of several reasons to junk Rove’s majority scenario.

Among the factors driving the urban growth spurt are a desire by young people to live closer to the urban core than the urban frontier, high gas prices and the toxic housing and lending environment. More American live alone than ever before — about 33 million people, 28 percent of all households — and most of them live in cities. Solitary living and coupling without children are the top two residential choices, according to the Census Bureau.

When Sarah Palin talked on the campaign trail about the “real America,” she was referring to a shrinking one.

All of which bodes well for Democrats, the urban party. Obama won 21 of the 25 largest metro areas in 2008. Among population clusters in swing states, he carried the Denver metro area by 17 points, Las Vegas metro by 19 points and Orlando, the fastest-growing urban area in Florida, by 9. He also won the Tampa-St. Petersburg area, by five. Each of these showings were big moves for Democrats.

By winning the urban vote — which made up 30 percent of the electorate in 2008 – in such a lopsided manner, Democrats could afford to lose rural areas, which were 21 percent of the overall vote. When Sarah Palin talked on the campaign trail about the “real America,” she was referring to a shrinking one.

The biggest prize is the suburbs, where half of all voters live. In 2008, Obama carried the suburbs by two points. The trends since the housing collapse have made older suburbs denser, and thus more likely to vote Democratic in the minds of some strategists.

Racial diversity, and the need for more government services and infrastructure, tend to make the older suburbs more like cities in their voting behavior, said Ruy Teixeira, who has written extensively about changing election demographics.

Teixeira has been predicting an emerging Democratic majority since 2002 – based on voting trends of young people, ethnic minorities and white, college-educated city dwellers. In polling for this year’s presidential election, Obama is doing even better with Latinos than in 2008, and holding a strong lead (though down a bit) with the youth vote. The new population figures have only fortified Teixeira’s view.

At the same time, turnout in this year’s Republican primary has been dominated by aging white male voters, not exactly a roadmap for the future, given the trends.

Republicans were crushed in the first two tiers of suburbia in 2008 – that is, the more settled communities. Obama lost what Teixeira called “emerging suburbs,” but made sizeable gains for his party from the 2004 election.

It was only in far exurbia that Republicans showed real strength in any kind of urban setting. And exurbia, Teixiera said in an interview, makes up only 3 percent of the vote.

But before these Home Depot-cluttered counties can be painted blue, some caution is in order.

It’s misleading to think the exurban frontier is closed, or even emptying out. What has settled down is the growth rate. Americans have always pushed out. Even if greater Phoenix is no longer growing at the rate of an acre an hour, as it was during the peak of its expansion, that particular phoenix will no doubt rise again, given the lure of the Sunbelt.

Low interest rates, stable gas prices and a bounce back in the housing industry could bring fresh life to the far fringes.

And Texas, the biggest and one of the fastest growing of Republican-dominated states, defied the trends of other red states that saw stagnant exurban growth. Of the 20 fastest growing metro areas over the last two years, four of them are in Texas.

And don’t forget the 2010 midterm election, when Tea Party fervor overwhelmed many of the positive trends for Democrats and returned Republicans to power in the House.

Still, for Democrats, the geography of tomorrow is the urban renaissance – a boundary that now includes big parts of suburbia.

An earlier version of this article misstated the results of the 2008 election in Loudoun County, Va.; it was won by President Obama, not Senator McCain.