But as the chase for the 2008 Democratic presidential nomination intensifies, the high-wire act of political purity is becoming more difficult for him to maintain, particularly on days when the race takes on the air of a bare-knuckles street fight.
The latest episode unfolded Thursday. As Mr. Obama spent a rare day in the Capitol, researchers at his headquarters in Chicago distributed a document that directly — and sharply — took aim at Senator Hillary Rodham Clinton.
It was, of course, in a similar vein and tone as documents prepared by any sophisticated political operation. But is there a different standard for Mr. Obama, who pledged to run a new kind of campaign?
“In this business, half the time we are being attacked for not being tough enough, and now we’re being attacked for being too harsh,” said David Axelrod, the campaign’s chief strategist. “The truth is that this is a tough, competitive business.”
And Mr. Obama, of Illinois, is finding out just how tough.
In Chicago, he has been dogged about his friendship with a businessman indicted on federal charges of business fraud and influence peddling. (A columnist for The Chicago Sun-Times declared: “suddenly this gleaming presidential hopeful and paragon of new politics behaves just like any other dissembling, dismissive Chicago pol, ducking the discussion while pretending not to.”)
Earlier this year, his campaign mixed it up with the Clinton campaign over remarks made by David Geffen, the entertainment industry executive, leading Mr. Obama to urge his staff, as he put it, “to be careful not to slip into playing the game as it customarily is played.” The Clinton campaign called on Mr. Obama to distance himself from Mr. Geffen after he suggested that Mrs. Clinton was unelectable and Mr. Clinton untrustworthy.
The political brawls that become public are just one manifestation of a less-visible battle conducted through competing opposition research teams that employ real and not-so-real scandal, changed policy positions and old and new relationships with people whose reputations are less than sparkling to try to shape news coverage and impressions of the candidates.
Barely a day passes when campaigns do not prepare documents against their rivals, excerpt the flashiest passages and shop them around to political reporters or bloggers, hoping someone will bite. Competing campaigns respond in kind, hoping to deflect possibly damaging bullets. Journalists sometimes play along, picking up a phrase, a nugget of information or a perspective that furthers the agenda of one side or another.
Much of this drama unfolds behind the curtains of today’s technologically driven political campaigns. But the curtain was pulled back this week, at least for a moment, when a document prepared by the Obama campaign landed in the hands of the Clinton campaign.
Referring to various ways in which Mrs. Clinton, of New York, and her husband had benefited, financially and politically, from support from Indian-Americans and companies that do business in India, the Obama campaign circulated a document to reporters on the basis that they not reveal where it had come from. Under a bold headline, the document referred to Mrs. Clinton as “(D-Punjab).”
The Obama campaign was forced to acknowledge authorship when the Clinton campaign got a copy and shared it with The New York Times.
For the Clinton campaign, drawing attention to a document attacking its own candidate had the effect of demonstrating that Mr. Obama, like other candidates, is not above a bit of political street fighting and, by implication, should not be allowed to cast himself as a champion of a purer version of public service. But in this case, the disclosure also threatened to create a substantive problem for Mr. Obama by leading an Indian-American group to accuse Mr. Obama of engaging in racial stereotyping.
“As representatives of the Indian-American community, we have been encouraged by your message of inclusion and your promise to bring a new kind of politics to our country,” Sanjay Puri, chairman of the US India Political Action Committee, said in a letter to Mr. Obama. “This is why we are so concerned about media reports indicating your staff may be engaging in the worst kind of anti-Indian-American stereotyping.”
In a statement on Friday, the Obama campaign expressed its regret.
“Barack Obama has been a longtime friend of the Indian-American community and our campaign is fortunate to have strong support from Indian-Americans across the country,” said David Plouffe, the campaign manager. “The intent of the document was to discuss the issue of outsourcing, but we regret the tone that parts of the document took.”
Mr. Obama declined an interview request.
The mini-furor over the opposition research documents highlights the intensity and fragility surrounding the fight for the Democratic presidential nomination. And it highlights the challenges for Mr. Obama as he pursues his quest to embrace a new kind of politics in a campaign operating under the old rules of politics, where every deviance and every negative word is almost certain to be seized upon.
“Will we be judged by a different standard? We have, in many ways, held ourselves to a different standard,” Mr. Axelrod said, but added: “When they throw the stink bomb at you, you can’t be caught unaware.”