Barack Obama was a religious sceptic with an identity crisis when he first heard the Rev Jeremiah Wright preach back in 1982.

During the sermon something strange happened: the pastor’s words of hope stirred Obama’s insight that the stories of ordinary black people were his own story, and he felt a profound desire to “give oneself up to God”. Tears streamed down his cheeks.

It may be one of fate’s cruelties that Wright, who became a father figure to the fatherless Obama, could go down in history as the man whose incendiary rhetoric helped to prevent the young Democratic politician from becoming the first black president of the United States.

Friendship with the 66-year-old Chicago cleric, who blessed the marriage of Obama and his wife Michelle, baptised their daughters and helped the young mixed-race man to understand himself as an African-American, is now taking a toll on Obama’s chances of beating Hillary Clinton to the Democratic nomination. Polls last week showed his once-formidable 20-point lead in North Carolina, whose primary is on Tuesday, had been cut to between 5-10%.

The falling out between the two men, after videos of Wright’s most outrageous utterances (notably “God damn America”) were spliced together and replayed in an endless loop on news channels, came to a head last week. The unrepentant pastor came out fighting, flanked by some of the most divisive figures in black America, including Marion Barry, Washington’s disgraced former mayor, and Malik Zulu Shabazz of the New Black Panther party.

Wright defended his remark about “chickens coming home to roost” on September 11. He called Louis Farrakhan, the acting head of the Nation of Islam, “one of the most important voices in the 20th and 21st century”. He evoked whites going to morning worship and putting on Klan sheets at night. He defended his claim that the US government invented the HIV virus to decimate blacks.

Obama is reported to have felt stunned and betrayed, particularly by his mentor’s suggestion that the presidential candidate privately agreed with him. In March Obama seemed to have defused the uproar over his association with Wright by comparing him to an “old uncle” who sometimes says disagreeable things. His nuanced speech about race in America won praise. He refused to disown his friend, but last week he felt compelled to denounce him: “Whatever relationship I had with Rev Wright has changed.”

Wright, a leading exponent of prophetic oratory in the style of Martin Luther King, predicted the schism with Obama a year ago. “If Barack gets past the primary, he might have to publicly distance himself from me,” he told The New York Times.

However, he appears to have been stung when Obama did just that. The disengagement began when Obama declared his candidacy in early 2007. Wright, invited to deliver an invocation at the event, was told the evening before that he was being stood down. According to Wright, Obama told him: “You can get kind of rough in the sermons. Rather than have you out front, we thought it would be best to not have you do the invocation.”

As he found himself edged out further, Wright directed his ire at Obama’s political adviser, David Axelrod, a white Chicago political operative.

Some commentators blame Wright’s ego for the spiralling row. “It’s easy to hurt his feelings,” said Richard Sewell, one of Wright’s deacons. After all, he has just retired after 36 years as pastor to the Trinity United Church of Christ in inner-city Chicago, during which time his congregation exploded from 87 to nearly 10,000, making it the denomination’s largest. A much sought-after figure, loaded with honours, he remains one of the country’s most dynamic preachers. Proud of having served his country, he was suddenly being cast as an unpatriotic pariah.

Others detect jealousy of his former protégé’s effortless rise. But at the heart of the estrangement lies a generational struggle in the black community. Whereas Obama exhorts Americans to heal their racial wounds and transcend their differences, Wright cannot forget them.

Like the Democratic activist Jesse Jackson, he repeatedly invokes perceived injustices. This can sound like paranoia – though Wright’s assertion of an HIV plot against blacks stems from the notorious Tuskegee medical experiment in 1932, when 399 black men in the late stages of syphilis were deliberately left without proper treatment.

“The whole generation that Rev Wright represents is expressing what they call a righteous anger, the anger from the failed promises of America,” said Dwight Hopkins, a professor at the University of Chicago divinity school. This plays to white fears of the angry black man and the economic competition he represents. But Wright does not focus exclusively on white America, according to Martin Marty, a retired professor of religious history: “He is very hard on his own people. He criticises them for their lack of fidelity in marriage, for black-on-black crime.” Wright, who is married to Ramah, has four daughters, a son and three grandchildren.

In his speech on race, Obama tried to excuse the minister’s denunciations of America by saying that for blacks of his generation, memories of “humiliation and doubt and fear have not gone away”.

However, Wright’s background was one of comparative privilege.

He was born in Philadelphia on September 22, 1941, the son of Jeremiah, who for 62 years was pastor at Grace Baptist church in Germantown, a racially mixed area of largely middle-class families. His mother, Mary, was the first black to teach at Germantown high.

Rather than attend the more racially mixed high school where his mother taught, Wright travelled a few miles to the elite Central high school. The student body was then 90% white and about three-quarters Jewish. Former students attest to the absence of racial tension. One of them, the black comedian Bill Cosby, said Central was “wonderful”.

School reports noted that Wright was “the epitome of what Central endeavours to imbue in its students”. In 1961, after two years at Virginia Union University, he was inspired by President John F Kennedy’s challenge: “Ask not what your country can do for you, but what you can do for your country.”

Waiving his student deferment, he left college and joined the Marine Corps as a private. As he pointed out last week, this was in stark contrast to Vice-President Dick Cheney, who in the same period received five deferments.

In 1963, after two years of service, Wright transferred to the US Navy to train as a cardiopulmonary technician. He was assigned to the medical team charged with the care of President Lyndon B Johnson after his surgery in 1966 and received three commendations before he left the next year.

Wright enrolled at Howard University in Washington DC, earning a master’s degree in English before studying at the University of Chicago divinity school. In his memoir Dreams from my Father, Obama painted an intriguing picture of Wright “dabbling with liquor, Islam and black nationalism in the Sixties” before his faith reasserted itself.

He became pastor at Trinity in 1972, quickly galvanising a small, demoralised congregation and bump-starting an outreach scheme that spawned 70 programmes targeting youth and the community. Under Wright, Trinity was a progressive church that welcomed gays and lesbians while embracing Aids sufferers at a time when many black churches shunned them.

In his autobiography Obama recalled their first meeting. Then a young community organiser waiting to go to Harvard Law School, Obama was contacting a number of ministers, but was struck by Wright’s apparent ability to hold together conflicting strains of the black experience. “ ‘We’ve got a lot of different personalities here,’ he told me. ‘Got the Africanist over here. The traditionalists over here. Once in a while I have to stick my hand in the pot – smooth things over before stuff gets ugly’.”

Things have got ugly, and the question for Obama is whether his old friend will continue to stir the pot. Republicans are resolved to remind people of Wright’s provocative comments if Obama wins the Democratic nomination. And many believe that Wright is not about to leave the stage quietly.

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