Chicago pastors still remember Obama making the rounds of local churches and conducting interviews—in organizing lingo, "one-on-ones"—where he would probe for self-interest. The Reverend Alvin Love, the Baptist minister of a modest brick church amid the clapboard bungalows of the South Side, was one of Obama's first one-on-ones. During a recent visit to his church, Love told me, "I remember he said this to me: There ought to be some way for us to help you meet your self-interest while at the same time meeting the real interests and the needs of the community.'" . . .

He was sometimes more interested in connecting with folks on the South Side than organizing them. He studied the characters he encountered so closely that [fellow organizer Mike] Kruglik says Obama turned his field reports into short stories about the hopes and struggles of the local pastors and congregants with whom he was trying to commune.

Where some of Alinsky's disciples speak of his work with religious fervor, Obama maintained some detachment during these years. . . .

As it was, he ran into the same roadblock as his trainers had. "Obama," Galluzzo told me, "was constantly being harassed by people saying, Oh, you work for that white person.'" On one occasion, he eagerly tried to make his pitch about joining DCP [Developing Communities Project] to a Reverend Smalls. Smalls wasn't interested. "I think I remember some white man coming around talking about some developing something or other," he told Obama. "Funny-looking guy. Jewish name." His hostility only grew when Obama explained that Catholic priests were also involved. "Listen ... what's your name again? Obamba?" Smalls asked without waiting for an answer. "Listen, Obamba, you may mean well. I'm sure you do. But the last thing we need is to join up with a bunch of white money and Catholic churches and Jewish organizers to solve our problems." Obama left the meeting crestfallen.

On a Sunday morning two weeks before he launches his presidential campaign, Obama is at Trinity United Church of Christ on the South Side, gently swaying from side to side under a giant iron cross. From the outside, the church looks more like a fortress than a house of worship, with high whitewashed brick walls topped with security cameras. Inside, Trinity is the sort of African American community that the young Obama longed to connect with when he first came to Chicago. The church's motto is "unashamedly black and unapologetically Christian," and sunlight streams through stained glass windows depicting the life of a black Jesus. The Reverend Doctor Jeremiah A. Wright Jr., Trinity's pastor since 1972, flies a red, black, and green flag near his altar and often preaches in a dashiki. He has spent decades writing about the African roots of Christianity, partly as a way to convince young blacks tempted by Islam that Christianity is not "a white man's religion."

On this particular Sunday, the sea of black worshippers is dotted with a few white folks up in the balcony, clutching copies of The Audacity of Hope they've brought for Obama's book-signing later. Obama, sitting in the third row with his wife and two daughters, Malia and Natasha, stands, claps, prays, and sways along with the rest of the congregation. During the sermon, he watches the preacher carefully and writes notes. When asked by Wright to say a few words, Obama grabs the microphone and stands. "I love you all," he says. "It's good to be back home." The 150-person choir breaks into a chorus of "Barack, Hallelujah! Barack, Hallelujah!"

This adulation is a far cry from how Obama was received by Wright when they first met in the mid-'80s, during Obama's initial round of one-on-ones. Like Smalls, Wright was unimpressed. "They were going to bring all different denominations together to have this grassroots movement," explained Wright, a white-haired man with a goatee and a booming voice. "I looked at him and I said, Do you know what Joseph's brother said when they saw him coming across the field?'" Obama said he didn't. "I said, Behold the dreamer! You're dreaming if you think you are going to do that.'"

A Reverend Philips put the problem to him squarely when he learned that Obama didn't attend services. "It might help your mission if you had a church home," he told Obama. "It doesn't matter where, really. What you're asking from pastors requires us to set aside some of our more priestly concerns in favor of prophesy. That requires a good deal of faith on our part. It makes us want to know just where you're getting yours from."

After many lectures like this, Obama decided to take a second look at Wright's church. Older pastors warned him that Trinity was for "Buppies"—black urban professionals—and didn't have enough street cred. But Wright was a former Muslim and black nationalist who had studied at Howard and Chicago, and Trinity's guiding principles—what the church calls the "Black Value System"—included a "Disavowal of the Pursuit of Middleclassness.'"

The crosscurrents appealed to Obama. He came to believe that the church could not only compensate for the limitations of Alinsky-style organizing but could help answer the nagging identity problem he had come to Chicago to solve. "It was a powerful program, this cultural community," he wrote, "one more pliant than simple nationalism, more sustaining than my own brand of organizing."

As a result, over the years, Wright became not only Obama's pastor, but his mentor. . . . Wright is one of the first people Obama thanked after his Senate victory in 2004, and he recently name-checked Wright in his speech to civil rights leaders in Selma, Alabama.

The church also helped Obama develop politically. It provided him with new insights about getting people to act, or agitating, that his organizing pals didn't always understand. "It's true that the notion of self-interest was critical," Obama told me. "But Alinsky understated the degree to which people's hopes and dreams and their ideals and their values were just as important in organizing as people's self-interest." He continued, "Sometimes the tendency in community organizing of the sort done by Alinsky was to downplay the power of words and of ideas when in fact ideas and words are pretty powerful. We hold these truths to be self-evident, all men are created equal.' Those are just words. I have a dream.' Just words. But they help move things. And I think it was partly that understanding that probably led me to try to do something similar in different arenas."

In 1995, Obama shocked his old friend Jean Rudd by telling her he wanted to run for the state Senate. Back in 1985, Rudd, then working at the Woods Fund—a Chicago foundation that gives grants for community organizing—had provided Kellman with his original $25,000 to hire Obama. When Obama returned to Chicago to practice law, he joined the board of Rudd's foundation. Now he was going to the other side. "That's a switch!" she told him. Obama insisted that nothing would change. "Oh no," he said, according to Rudd. "I'm going to use the same skills as a community organizer." . . .

But when those supporters become a liability, Obama has not been afraid to take a direct, confrontational approach. Reverend Wright learned this recently, on the evening before he was scheduled to deliver the invocation at Obama's presidential announcement speech in Springfield. According to The New York Times, after Trinity's Afrocentrism—which had originally drawn Obama to the church in the 1980s —had become a sticky campaign issue, Obama called his old friend and told him it was probably best if the pastor didn't speak, after all. The following day, Wright could be seen silently watching the proceedings from the sidelines along with other Obama supporters. . . .

In our last conversation, . . . I asked Obama if his reputation for purity is a little overblown. He chuckled "I wouldn't be a U.S. senator or out of Chicago or a presidential candidate from Illinois if I didn't have some sense of the world as it actually works," he said. "When I arrived in Chicago at the age of twenty-four, I didn't know a single person in Chicago, and I know an awful lot of folks now. And so, obviously, some of that has to do with me being pretty clear-eyed about power."