At least nominally, a conflict of interest with a foreign client, not bad strategy, cost Mark Penn his perch atop Hillary Clinton's message machine.

Still, Penn is widely blamed for the Clinton campaign's struggles, having dictated the campaign's reliance on "inevitability" and "experience," and rejecting the need to establish the candidate's "likeability."

Penn's biggest lapse, however, may have been his failure to correctly apply his signature approach, the creative segmenting of the electorate. This allowed Barack Obama's campaign to artfully leverage support from small groups who swing great weight in the limited universe of Democratic primary and caucus voters.

Penn gained national notice when Dick Morris handpicked his polling firm, Penn Schoen & Berland—a 20-year fixture in New York City's rough political world—for Bill Clinton's 1996 reelection team. President Clinton's comeback victory helped Penn Schoen & Berland attract major corporate clients while continuing its work for politicians like Hillary Clinton, Al Gore, and Michael Bloomberg, all of whom spent lavishly on polling.

(I was a client—a happy one, I should note—of a unit of Penn Schoen & Berland that provides research services to Condé Nast Publications, which owns Portfolio.com, and I once worked—also happily—for Geoff Garin, the pollster newly selected to replace Penn on Clinton's campaign.)

In 2001, advertising conglomerate WPP Group bought Penn Schoen & Berland. Penn became C.E.O. of Burson-Marstellar, the WPP-owned public relations and lobbying giant, a position he has juggled with his work on for Clinton.

On March 31 he met with the Colombian ambassador to the U.S., a Burson-Marstellar client, to map a strategy to persuade Congress to pass a bilateral trade agreement with Colombia. Senator Clinton opposes that pact, and has made doubts about free trade an issue in her tight primary race in Pennsylvania.

In the ensuing firestorm, Penn had to resign as chief strategist for Clinton.

What was surprising about Penn's tenure with Clinton's campaign is not the conflict that ended it (talented campaign strategists often lend their skills to corporate clients between election cycles), but Penn's failure to apply his own theories as well as the opposition did.

Penn is the best-selling author of Microtrends: The Small Forces Behind Tomorrow's Big Changes. This book mirrors his approach to elections: identify influential archetypes, like 1996's Soccer Moms, and fine-tune campaign proposals (for example, requiring parental-control "V-chips" in all new TVs) to win them over.

Microtrends applies this analysis to the social sphere: Penn's "microtrends" involve tiny but visible segments of the population who are growing in size or influence due to social and economic forces—like the 1 percent of California youths who list "sniper" as a career goal.

The book's critical reception was mixed. While it gained some corporate cachet, political writers showed Penn no love. Influential blogger Ezra Klein called Microtrends "so epically awful as to take the entire polling industry down with it." Maureen Dowd snarked that "the chapters all read like reports that Mr. Penn wrote for clients," and compared the names he gave his population segments—among them Shy Millionaires, Mildly Disordered, and Uptown Tattooed—to "a new lineup of Fox reality shows."

But perversely, Obama's success has vindicated Penn's microtargeting approach. This year, microconstituencies that could easily have fit Penn's book were poised to make a huge splash in the relatively small Democratic primary pool, swelling 2004's turnout of 16 million by 80 percent.

(Primary and caucus voters are a small, skewed fraction of those who cast ballots in November, estimated at 122 million voters in 2004 and certain to grow this year.)

Receptive to messages of inspiration, change and political reform, groups like newly energized Internet donors, nostalgic middle-aged liberals, freshly recruited pundits, and atypically upscale independents have provided Obama's keys to success.

Online Donors.

Foremost among the influencers are a new wave of political donors, who have always been a microconstituency. Most Americans donate to charitable causes like churches, medical research, even pet rescue—not political candidates. The total number of donors to all presidential candidates in 2004 totaled just one million—less than 0.5 percent of the adult population. But the Web has caused this smallish universe of political donors to rise sharply: Obama's backers now claim that, if nominated, he alone will attract two million donors by November.

These new donors' influence goes far beyond the attitudes changed by the ads they fund. They have rewritten the rules about how quickly a candidate can capitalize on sudden momentum, and pumped previously unseen amounts of cash into the campaign industry. These new online donors are perfect specimen of a Penn microgroup: small, but growing rapidly as a result of new outside forces (the Internet, here).

The Obama campaign's message perfectly suits the motivation of the kind of person who puts money behind a candidate: the desire to be part of history—a claim Clinton could have made as well, but rejected in favor of the "inevitability" approach. How many people are inspired to donate to the inevitable?

Political Junkies.

Once, political aficionados were too few for their votes to have noticeable impact, and surveys showed voters rarely based their choices on strategic considerations. But their ranks have risen ever since Theodore White's 1961 book The Making of the President, 1960 invented the mass market for political strategy.

This year, that audience is expanding thanks to a plethora of inside-baseball politics programs on three cable news networks and a growing stream of political websites. (They're still a microconstituency: the peak audience for a top political chat show is well below two million.)

Political views aside, these aficionados share an obsession with the rules of the game, the ups and downs of the daily news cycle, and process and story-line rather than policies. This year, it seemed that every undecided Iowan interviewed at a rally was second-guessing the candidates' strategies or weighing their "electability."

Dedicated political hobbyists could easily tip the scales in a state where, even in this record year, Democratic caucus turnout was just 250,000. Relatively upscale and educated, they can indulge their political passion by volunteering, attending rallies, donating, and, of course, voting.

Obama's history-making quest proved far more appealing to political junkies than Hillary's theme of the steady workhorse. Politicos love an exciting contest, and hate "inevitability"—and may now rally to Clinton only after it appears some are trying to force her from the race.

Entry-Level Pundits.

The steady increase in programming hours, columns, and websites devoted to political strategy fuels an ever-growing demand for analysts and bloggers who can explain the election.

Many local newspapers now have their own political blogs, while TV and talk radio need ever more guests with some pretence to political expertise. Even amateurs can get into the act, by commenting on blogs (or clawing their way into a Frank Luntz focus group).

But, rather than making political analysis more diverse, the relative inexperience of the expanded punditocracy, and their exuberance for the "horse race," produces more pack journalism. The conventional wisdom becomes more entrenched, skewing the information that flows to voters.

This year, Obama stoked media excitement that translated into a constant message over the airwaves. The Clinton campaign seemed to ignore this rising class of political interpreters, making no attempt to court them—in fact, infuriating them with a heavily packaged campaign that played into their stereotypes, and mocking the pundits' very purpose by claiming Clinton's victory as "inevitable."

Independent Crossovers.

Independents who vote in Democratic primaries aren't "typical" independents: they're more upscale, and much more politically engaged.

One stubborn barrier to the long-awaited development of a third party in the U.S. has been the reality that self-described independents agree upon almost nothing; a surprising majority of them are downscale, poorly informed and disengaged with politics.

A much smaller group fits the stereotype of the thoughtful, nuanced independent: liberal on social issues, perhaps, but fiscally conservative. These are the ones who might cross over to vote in a Democratic primary.

The one thing most independents do have in common is visceral dislike for the major parties. This is why Obama's message of post-partisanship works so well for them. Independents who vote in primaries tend to be well informed and engaged with the political process. They are predisposed to Obama's central themes, which concern politics itself (activism, unity, reform) and are more concerned with Hillary's campaign tactics than her policy proposals.

This year, the importance of states with open primaries has given the upscale independent voter new leverage; the relatively small electorate gives them large potential impact if they break a particular way. In Virginia and Wisconsin, nearly one in three Democratic primary voters were independents or Republicans; exit polls showed they tilted heavily toward Obama.

Weepy-Eyed Boomers.

Not every Baby Boomer is a nostalgic liberal or ex-Yippie. The "great silent majority" shunned the demonstrations and sit-ins. But the early Boomers for whom late '60s activism was formative are a small but visible group, now at the peak of its influence. Many of them are politicians, journalists, or donors.

For many of them, the wounds of the seminal year of 1968 never healed. Those who chanted "the whole world is watching" saw their hope and excitement dissipate. The promise of that slogan was never fulfilled, and as these children of the '60s start to enter their 60s, their sense of unfinished business takes on urgency.

Now Obama—seemingly Robert F. Kennedy and the Rev. Martin Luther King rolled into one—offers them a two-for-one redemption of 1968's political assassinations and the illusion of picking up where America left off.

The Obama campaign has fed the fantasy, converting their iconic Kennedy endorsements into a Camelot video ad. Meanwhile, Hillary—a genuine icon from that era, thanks to her Wellesley commencement address, which Life magazine profiled in 1969—neglected to offer her contemporaries any sense of completing the mission of their youth.

Quarterlife Activists.

It would be a mistake to believe that the typical 21-year-old can be found chanting "Yes We Can" at an Obama rally. Every post-'60s generation has seen its own popular cause sweep a certain segment of the young: anti-nuclear power in the 70's, apartheid in the '80s, globalization in the '90s. For all their visibility, these were fringe phenomena—most Americans aren't eager to join a movement.

But some are. After Vietnam, no youth cause translated into electoral politics until 2004, when Howard Dean managed to harness the idealism and the need to belong that characterizes the young and educated. He also pioneered the use of Web tools like social networking and blogging to channel that political energy. Obama offers young idealists a huge upgrade over Dean, with a better-focused message and a more inspiring delivery.

Still, 20-something activists may be the one group that Penn and the Clinton campaign can be excused for missing. Hillary's every-mom appeal is light years away from the idealistic dreams of a young Obama supporter, and probably no one attends a Clinton event in hopes of hooking up.

But considering the accusations that Penn had almost microtargeted the Clinton campaign into oblivion, it's ironic how thoroughly he missed the importance of so many small groups that did so much to benefit her opponent.

He provided no mechanism to harness the enthusiasm of online donors, no redemptive vision for nostalgic boomers, no sense of fresh thinking for upscale independents, and, until late in the game, no exciting storyline for the political junkies and entry-level pundits.