Pennsylvanians are going to have a much bigger-than-usual role in determining the Democratic nominee this time around. Pundits say the key to the race lies in the traditional fault lines of race, gender and generation. A recent story in The Wall Street Journal featured a map of the so-called "three Pennsylvanias" -- with the "older lower west" and the conservative central regions inclined toward Hillary Rodham Clinton, and the "more affluent, diverse east" breaking for Barack Obama.

Mr. Obama now appears to be closing what looked to be a huge gap in the public opinion polls just a couple of weeks ago. He continues to pull overwhelming support from greater Philadelphia's black community. But he also is drawing in new voters from the tens of thousands of college students in Philly, Pittsburgh, State College, the Lehigh Valley and other pockets across the state. He's also likely to do well in the affluent suburbs around several of the state's largest cities.

Mrs. Clinton, on the other hand, resonates with baby-boomers, seniors and especially with women. The Clinton campaign also gains support among union members in the state's historically blue-collar industrial districts, which have been hard-hit by deindustrialization and economic anxiety for years.

But what's seldom discussed and yet very interesting about the Pennsylvania primary and other venues in this election cycle runs deeper than the well-documented young vs. old, black vs. white or male vs. female dynamics. Both the Democratic nomination and the upcoming general election turn on an even more fundamental economic and social force -- class.

In 2002, I defined a new creative class of inventors, entrepreneurs, engineers, artists, musicians, designers and professionals in idea-driven industries. This observation was based on national and global trends, but it was significantly informed by the sharp and worsening class divide I observed in Pittsburgh and Pennsylvania.

Today, nearly 40 million American workers fit in the creative class -- 35 percent of the working population and a good deal more than the 23 percent who make up the working class. That the creative class drives economic success in cities and nations is undeniable; today's leading regions in innovation and economic growth -- from the Boston-New York-Washington corridor to greater San Francisco and the Pacific Northwest -- are prospering because they are magnets for the talented and entrepreneurial members of this class.

The massive migration of talent and energy and the consequent demographic sorting by income, ability and personality type is not only making America's economic geography more uneven and spiky (which is bad enough), it also shapes a deep class-based political polarization which splits the electorate and divides the Democrats in particular.

Up to this point, members of the creative class predominantly have cast themselves as politically independent or "post-partisan," and their political sympathies have been up for grabs. The traditional Republican platform of individualism, economic opportunity and fiscal responsibility appeals to them; so, too, the Democratic values of social liberalism, environmentalism and support for gay and women's rights.

Democratic candidates like Bill Bradley and Howard Dean attracted the creative class in the 2000 and 2004 elections. But no one has caught fire with this class like Barack Obama.

I knew it was time for a closer look when MTV called me to comment on the Obama and creative-class phenomenon. And I am not the only one analyzing it. After pouring through detailed exit poll data on race, income and ideological orientation, Chris Bowers, the netroots blogger, concluded: "When all is said and done, it looks like Obama will ultimately owe his victory to African Americans and his huge, creative-class activist army."

To get a better sense of how deep this support runs, I asked opinion pollster John Zogby to look into how creative-class people were voting in this primary season. The result: On issue after issue, they preferred Barack Obama to either Hillary Clinton or John McCain by wide margins.

Asked which presidential candidate would "provide meaningful leadership for the country," 64 percent of creative-class respondents supported Mr. Obama, compared to 21 percent for Mrs. Clinton and 9 percent for Mr. McCain. As to who was best positioned to unify the country, Mr. Obama was chosen by 74 percent of creative-class voters. The same pattern holds across the board: The creative class prefers Mr. Obama on issue after issue, from illegal immigration, to the economy, to health care. Mr. Obama even bests Mrs. Clinton and Mr. McCain substantially on his supposedly weakest issue -- "combatting terrorism" -- registering half of all creative-class support, compared to 24 percent for Mrs. Clinton and 18 percent for Mr. McCain.

What we're seeing is not a red state, blue state divide, but something bigger, if more calibrated. Mr. Obama consistently polls strongest in cities and regions with creative-class concentrations. Mrs. Clinton's edge is in older industrial areas and blue-collar towns, where voters are anxious about the economy and job prospects. This divergence raises an interesting dilemma for campaign strategists. Is a coalition between the creative class and working class viable?

Appealing to both would prove difficult. The creative class anticipates the future while the working class tends to seek protection from it. The creative class does not want someone to fight for them; the us-against-them approach doesn't resonate with them in politics any more than it does in a conference room, film studio or the skunkworks of a high-tech startup.

It would be difficult for Mrs. Clinton to win wholehearted endorsement of the creative class, as committed as she is to specific programs that its members might like. It also would be hard for Mr. Obama's general rhetoric of hope and change to win over those who are falling further and further behind economically.

In upcoming years, it will be vital for progressive political leaders to reach out to the working and service classes in ways that enable them to connect to the new creative economy. But in the short months remaining until the general election, deep-seated working-class anxiety about economic and social change is not likely to be overcome.

What's abundantly clear is that appeals to race, gender or age cannot provide the core support necessary for a lasting and sustainable political majority. Just as Franklin Delano Roosevelt forged a new majority on the swelling ranks of blue-collar workers, so must the party that hopes to win this election -- and shape the political landscape for years to come -- earn the enthusiastic support of today's ascending economic and political force -- the creative class.