ST. PAUL, Minn. — Sweeping demographic changes in the American electorate are undercutting old assumptions about swing voters and battleground states and making the 60-day general election campaign that started Friday even less predictable than usual.

Racial and ethnic diversity is spreading across the country. Aging baby boomers remain the biggest generational group in the electorate, but second in size are the millennials — 18- to 31-year-olds who have distinctive attitudes toward race and politics.

In the space of a generation, Americans have seen dramatic changes in the roles of women, the structure of families and the nature of the workplace. There has been a revolution in the technology that delivers information and knits communities.

Presidential nominees John McCain and Barack Obama personify that changing nation in striking ways. In age, race and life experience — even in use of emerging technology in the campaign — they mirror a nation in transition.

Some analysts are predicting that the 2008 election, like the one in 1980 that set the nation on a more conservative course, looms as a landmark contest in which the country is receptive to dramatic change.

"This is a pivotal moment in the sense that the politics is catching up to the demographic changes," says William Frey, a Brookings Institution scholar who analyzes population trends.

Democratic pollster Geoffrey Garin calls Democrat Obama — who's 47, biracial and multiethnic — "the face of the new generation" who has mobilized millions of younger voters this year.

But Garin notes that some, especially older white voters, find Obama's message and background — he is a first-term Illinois senator who spent nearly as long as a community organizer as he has in Congress — unpersuasive and even discomfiting.

In contrast, Republican McCain, a 72-year-old white man and decorated Navy veteran, has represented Arizona in the Senate for a quarter-century.

Their messages contrast, too: McCain attacks Obama for inexperience ("Is he ready to lead?" Republican ads ask) while Obama promises change from what he says are eight years of failed leadership by Republicans.

In some ways, cultural trends have helped both candidates.

Obama's hope of becoming the first black president has been boosted by younger voters who are less polarized about race than their elders; his candidacy probably wouldn't have been realistic a quarter-century ago.

Changing attitudes about age have helped McCain, who would be the oldest president elected to a first term.

"We no longer say someone is too old or too young" for a job, says Bernadette Budde, a political analyst with the Business Industry Political Action Committee. "We have a culture that believes Tony Bennett and Miley Cyrus have equal amounts to contribute to the world of song."

Both candidates have balanced the demographic makeup of their tickets with their choices of running mates.

McCain picked Alaska Gov. Sarah Palin, a working mother 28 years his junior whose husband is part Alaska Native. Obama picked Delaware Sen. Joe Biden, a white man and six-term senator who is 18 years older than him.

Even so, national campaigns are usually all about the top of the ticket. Will the McCain-Obama election be a turning point in American politics?

Some analysts say yes.

The 2008 race will "prove in part to be a decisive political contest between the old America and the new America. Between the thing we were, and the thing we have been becoming for 40 years or so," Peggy Noonan, a White House speechwriter for former president Ronald Reagan, wrote in The Wall Street Journal in June.

Democratic pollster Celinda Lake sees Obama and Palin as examples of the sorts of candidates who increasingly will emerge in American politics. "This is really the first campaign of the 21st century," she says.

DEMOGRAPHIC DESTINY

Major demographic changes have shaped and reshaped American politics throughout the nation's history.

Andrew Jackson's election in 1828, which forged the modern Democratic Party, reflected the rise of a broader and more raucous democracy as the nation's boundaries pushed west and property was no longer a requirement for voting.

A century later, in 1932, Franklin Roosevelt tapped support from the growing ranks of Irish-American, Italian-American and other ethnic voters as part of a liberal political alliance that would hold the White House for 28 of the next 36 years.

That FDR coalition, which began to crack in 1968, collapsed with Reagan's election in 1980.

The California governor was helped in that campaign by population shifts into the South and West, and to the suburbs from big cities. The South became a GOP stronghold as white voters abandoned the Democratic Party.

Reagan's conservative alliance has held the White House for 20 of the past 28 years.

There are parallels between this year's election and the one that launched Reagan's presidency almost 30 years ago.

In 1980, as now, voters were anxious about the economy and gas prices. A foreign-policy quandary — then, the Iranian hostage crisis, now the Iraq war — contributed to their unease. Support for the incumbent party, then the Democrats, was undercut by voters' desire for change.

This time, McCain represents an incumbent Republican Party, but he emphasizes his own desire for change and distances himself from President Bush. Like President Jimmy Carter did in 1980, McCain attacks his opponent as a risky choice who offers what he calls "the wrong kind of change."

In another similarity to 1980, key groups in the electorate are up for grabs. Reagan attracted white working-class voters in the Midwest, many of them union members, who traditionally had voted Democratic.

Since then, those so-called "Reagan Democrats" have become part of the Republican base.

This time, Hispanics, the nation's fastest-growing ethnic group — since 1980, they have more than doubled as a percentage of the population — are fiercely contested. Bush did better than previous Republicans among Hispanics in 2004, but Obama now has a 40-point advantage among them, according to surveys by the nonpartisan Pew Hispanic Center.

Younger voters make up another key group. Obama's appeal among them has created the widest generation gap since political polling became routine a half-century ago. Voters under 30 are Obama's strongest age group, the USA Today/Gallup Poll shows. Voters 65 and older are McCain's strongest age group.

SHIFTING POPULATIONS

"Every growing demographic is trending Democratic and every shrinking demographic is trending Republican, from young people to Hispanics to you-name-it," says James Carville, an architect of President Clinton's 1992 victory. "The underlying shifts in demographics portend pretty good for Democrats in the future."

Former Massachusetts governor Mitt Romney, who sought the GOP nomination this year, says Republicans "have to be on the right side" of reaching out to growing numbers of minority and Hispanic voters. GOP positions on lower taxes, smaller government and greater school choices can help, he says.

In 1980, 14 percent of the nation's population was nonwhite. Now, one in four Americans are in minority groups. By the middle of the century, racial and ethnic minorities are projected to make up a majority of the U.S. population.

What's not clear is whether those demographic and other shifts have gone far enough to determine November's election.

Indeed, they have created a backlash among some voters. In a national survey of women sponsored by the advocacy group EMILY's List, one-fifth of those 63 and older called the nation's increasing racial diversity a negative trend. A similar number felt the same way about the Internet.

The changes in who we are, where we live, what we do and how we view the world have altered the political leanings of states once considered solidly in one camp or the other. The calculations by each candidate of what states he can count on and which ones he can contest are more complicated than they were even four years ago.

"The level of demographic change does have an impact," says Ruy Teixiera, editor of "The Future of Red, Blue and Purple America," being published this month. "These changes are destabilizing these states. Just because states voted one way a couple of elections ago doesn't mean they're going to stay that way."

WOOING NEW STATES

The last several elections have been marked by constancy: From the 2000 election to the 2004 election, 47 of the 50 states were consistently Republican or Democratic. Only Iowa, New Hampshire and New Mexico switched their electorate votes from one party to the other.

This time, however, the Obama campaign is trying to make far-reaching changes in the Democrats' map. Some states Democratic candidates traditionally target, including West Virginia and Arkansas, are getting relatively short shrift, but the campaign has run TV ads in 14 states that backed Bush in 2004.

"One of our goals is to wake up on Nov. 4 with as many paths to 270 electoral votes as possible," Obama campaign manager David Plouffe says, the number needed to win the election. The campaign has tried to build a "bigger battleground," in part by analyzing demographic changes in states that have a large number of black voters or have seen an influx of young people.

"Virginia, North Carolina, Montana, Alaska — only Sen. Obama could be competitive" in those states as a Democrat, Plouffe said. (He spoke before McCain picked Palin, presumably bolstering the GOP's hold on her home state.)

McCain campaign manager Rick Davis outlines a much more traditional electoral map and scoffs at the idea that Obama can contest states such as North Dakota, Montana and Georgia, where the Democrat is now airing TV ads. The McCain camp predicts the contest will come down to familiar cliffhanger states such as Florida and Ohio.

Even so, both campaigns are focusing on the emerging Mountain West battlegrounds of Colorado, Nevada and New Mexico. An influx of young people and other newcomers to Colorado has made the Centennial State a particular bellwether this time even though it's gone Republican in nine of the past 10 elections.

Meanwhile, economic troubles in Michigan and Pennsylvania, particularly in heavy manufacturing, have roiled their economies and their politics. Both are prime targets for the GOP even though they have voted for the Democrat in every presidential election since 1992.

"The white working class is a declining demographic, but they're still a lot of people, a lot of voters," Teixiera says. Those voters, particularly older ones, weren't a receptive group for Obama in the primaries.

The GOP also hopes to win Wisconsin and New Hampshire, states that went for Democrat John Kerry in 2004 but where McCain's reformist message could resonate.

"Other elections were more predictable, where you could narrow down the number of states in which you campaign, and you could decide groups to write off — but you can't do that anymore," Budde says. "I don't think this election fits in a mold."