(FORTUNE Magazine) – Something strange is happening in Orange County, the Southern California paradise of beaches, amusement parks, and endless rows of postwar tract homes. There, in the very breeding ground of the conservative revolution, people have begun voting for Democrats. In 1996, voters in a district in the heart of the county threw out fire-breathing Republican Congressman Bob Dornan and replaced him with Democrat Loretta Sanchez. In 2000, Al Gore got a bigger percentage of the county vote than any Democrat presidential candidate since Lyndon Johnson in the landslide of 1964.

Gore still only got 40.4%, mind you, and no one is betting that John Kerry will beat George Bush in Orange County this year. But the county's evolution is emblematic of larger forces that are reshaping the political landscape. The competing efforts of Republicans and Democrats to capitalize on these shifts will have dramatic implications for social, economic, and foreign policy.

The question is, which party will succeed? Ruy Teixeira, a senior fellow at the Century Foundation in Washington, D.C., looks at Orange County and sees a Democratic future. He figures the party will get its Orange County majority in a decade or so, and sees similar trends in suburbs all over the country. In the 2002 book The Emerging Democratic Majority, he and journalist John Judis argue that a new metropolitan coalition of working women, minorities, and professionals will bring the Democrats victories for years to come.

Make no mistake, though. This business of projecting new majorities is a bipartisan one. Democrats like Teixeira rest their case on demographics; Republicans rely more on ideology. Both sides' arguments reflect the reality that American voters are in the midst of a major realignment. Since 1932, the nation has been governed by two durable, geographically diverse partisan majorities: The Democratic Roosevelt alliance of city-dwellers and Southerners, and the Republican Nixon-Reagan coalition of suburbanites and Southerners. Now, though, the dividing line between the two parties is this: The more rural your place of residence, the more likely you are to vote Republican. The more urban, the more likely you are to vote Democratic.

On its face, this city/rural divide puts Republicans at a disadvantage. In a country where 53% of the people live in metropolitan areas of one million or more, there's just no way to build a lasting national majority upon a rural base. No one has done it, in fact, since Andrew Jackson in 1828. The U.S. Senate is an exception; the overweighting of rural votes inherent in its structure means Republicans could rule the north side of the Capitol for decades. Even in the House, the way Democratic and Republican voters are scattered about the landscape (Democrats are squeezed closer together) helps the Republicans. But at the presidential level there are good reasons why, when Republicans talk about a new majority, they focus on ideas, not constituencies.

One such majority-forming idea, offered by Weekly Standard editor and Republican idea man William Kristol just after his party's convention: "a robust and bipartisan patriotism ... proud of American principle and willing to use American power." Patriotism certainly ishelping President Bush: American voters always rally around their leaders at times of external threat, and while misgivings about the Iraq war keep growing, the Democrats have struggled to enunciate a consistent alternative to Bush's aggressive response to the terror threat. One assumes, though, that this can't go on forever. Either the Republican anti-terror strategy will succeed, in which case Americans will feel less threatened and thus less likely to rally around the flag, or it won't, in which case voters might want to try some other approach.

Another path to Republican dominance, outlined in The New York Times Magazine in August by pundit David Brooks, would be to abandon the anti-Washington stance that characterized the party in the 1980s and 1990s and instead adopt a "progressive conservative philosophy" of activist but market-oriented government. That's an attractive vision, and would certainly win back some lost suburban voters, but it sounds awfully Clintonian. There's no reason a Democrat couldn't adopt the same strategy.

Hints of a more distinctly Republican path of attack can be found elsewhere in the Brooks oeuvre. In his new book, On Paradise Drive: How We Live Now (And Always Have) in the Future Tense,the Bethesda, Md., resident describes a trip outward from the center city (conveniently skirting poor urban neighborhoods): One starts at the urban "cool zone" and proceeds through the "crunchy suburb," the "professional zone" of the inner-ring suburb, the "immigrant enclave," and the postwar "suburban core" before finally landing in the bounteous, shopping-club-sated exurbs. This turns out to be a useful map of the territory through which the line dividing the two parties now runs. The inner three zones are all Democratic, except in Southern metro areas, where the Republicans have held on to the professional zone. The outer two have stayed Republican, except in a few big Northeastern and West Coast metro areas where all but the most distant exurbs are drifting Democratic.

The focus of Brooks's book, and of many Republicans' hopes and dreams, is on the booming exurbs. When I confronted Bush political guru Karl Rove with the evidence that lots of big, formerly Republican suburban counties have been going Democratic, he retorted, "That's only because of the changing nature of the suburbs. The cities are spilling out into the suburbs, the suburbs into exurban counties or smaller metropolitan areas." Those reliably Republican outer zones are growing so fast, Rove's reasoning goes, that they will offset the loss of a few close-in suburbs.

This argument appears to hold up in slow-growing Ohio and Pennsylvania, where immigrants aren't pouring in to replace fleeing urbanites and suburbanites. But it does not in California, which tipped to the Democrats in the 1990s, or in fast-growing Arizona, Nevada, Virginia, and Florida, which seem to be headed that way (as in so many other cases, fast-growing, increasingly Republican Texas doesn't fit the model). If they are not to be banished to minority status, the Republicans need to do more than just hold the exurbs. They must push back into the suburbs. The key to whether they can lies in those "immigrant enclaves" that Brooks, and most of his fellow Republicans, have tended to overlook. President Bush has been an exception, although he has muted his pro-immigrant message since 9/11.

Students of political shifts love historical parallels, and the closest at hand are those of the late 1960s, when Nixon aide Kevin Phillips wrote of The Emerging Republican Majorityand the Republicans established themselves as the preferred party of white America. But a more appropriate parallel for today's majority-makers may be 1896. That year, with the nation in depression and a Democrat (Grover Cleveland) in the White House, the party nominated William Jennings Bryan, who made lifting prices for farm products his chief campaign theme.

Bryan was a sincere advocate for the the poor, and his economic message electrified voters across the South and Great Plains. But neither it, his outspoken Protestant fundamentalism, nor his suspicion of both big cities and the outside world went over well with the industrial workers of the Northeast, Midwest, and West Coast--many of whom were Catholics or immigrants (or both), and almost all of whom lived in cities. Republican nominee William McKinley--a moderate Ohioan of great political skill--saw this, reached out to labor unions and immigrant organizations, and built an urban, industrial Republican majority that held (with the exception of Woodrow Wilson's presidency) until the 1930s.

Such a transforming election is the stuff of political operators' dreams, and McKinley is enjoying newfound acclaim. Onetime Republican strategist Phillips, now a Bush-bashing political independent, wrote a gushing McKinley biography in 2003. Karl Rove has emerged as a big McKinley booster as well. In 1997, Rove had to read through McKinley's papers for an assignment at the University of Texas (where he hopes someday to get a Ph.D. in government). He can't push the McKinley parallel too far: McKinley was, after all, the urban candidate. The states he won in 1896 were pretty much the same ones Al Gore won in 2000 (the fatal differences for Gore being that he lost Ohio and that Texas and Florida command a lot more votes now than they did in 1896). But one crucial step that McKinley took in 1896 is both possible and probably essential for any Republican out to build a lasting national majority: "He basically made it comfortable for urban ethnic working people to identify with the Republican Party," Rove says.

Today's "urban ethnic working people" are the recent immigrants from Latin America, Asia, and Africa who have settled in huge numbers in big American cities and, increasingly, their suburbs (racial and ethnic minorities now make up 27% of the suburban population nationwide, according to the Brookings Institution). So far most of them have felt more welcome in the Democratic Party--one reason why so many Democrats are doing so much better in many booming Sun Belt suburbs. If these immigrants and their children stick with the Democrats, the Republicans will be in deep trouble. But will they?

Consider, again, California's Orange County--home to just over 1% of the American people. Once lily white, the county is now 31% Hispanic and 14% Asian American. These newcomers, along with a growing number of affluent whites turned off by Republican social and environmental policies, are behind the Democratic gains in the county. But political majorities aren't the inevitable product of demographics. They also depend on the choices made by politicians along the way. And today's Orange County Republicans are making different choices than the John Birchers of yore. The Republican mayor of Anaheim, one of the county's two big cities, goes out of his way to court immigrant voters. A Republican Vietnamese immigrant from nearby Garden Grove is heavily favored to win a state assembly seat this November.

Ken Khachigian, an Orange County lawyer who was President Reagan's chief speechwriter, allows that Ruy Teixeira's prediction of an immigrant-fueled Democratic majority in the county might come true. But he doesn't think it can last. Already-affluent white professionals and upwardly mobile immigrants simply don't share the same interests. For example: Environmental groups and Democratic politicians are fighting a huge new housing development planned for the eastern part of the county--a place that would, if built, become home to lots of hyphenated Americans in search of lawns and good schools. Snorts Khachigian, himself a second-generation Armenian American: "These restrictionist, elitist policies of the left wing are not going to play well with immigrants." Then again, neither will all of the social and economic policies emanating from the Republican Party's rural, Southern base. To get a majority and keep it, both parties have to change. Since those changes would have to be in the direction of satisfying what has always been this nation's most important economic asset--its hardworking newcomers--that can't be a bad thing.