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.