Bob is fretting. The small steel thermometer he has dipped into the smoking oil is telling him it's too hot to start cooking the small blobs of batter that will soon be malasadas. Burned malasadas – the name Portuguese immigrants to Hawaii gave to what are essentially doughnuts – don't taste so good.

His stall in Kapiolani Park on the edge of Waikiki soon attracts a long queue of takers. But it is not just a good appetite that is drawing them. Everyone in this corner of the park this morning has come for another reason: to show support for a local boy who may be about to do something extraordinary; win the Democratic Party's nomination to be the first black (and first surfer) American President.

"Hot Obamasadas!" exclaim two large signs strung over the table where Bob is working. A lawn sign is planted in the ground next to him with a life-sized black-and-white headshot of a middle-aged African-American guy with familiar big ears and wide smile. A flower lei is hung around the photograph above the words, written in bright felt-pen colours, "Hawaii's Native Son".

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By rights, Barack Obama should prevail in caucus voting in Hawaii today and fatten slightly his delegate lead over Hillary Clinton. The remarkable early narrative of Obama's life – the child of a white woman from Kansas and a Kenyan father who abandoned the family when the boy was just two – mostly played out here in the Pineapple State, save for four years between the ages of six and 10 in Indonesia.

Hawaii imbued in Obama the quality that may be the most compelling of his candidacy. His promise to transcend racial and social differences. Few places better qualify as a true melting pot than Hawaii, its streets still teaming with a cosmopolitan mix of whites, Asians, Chinese, Japanese and (a few) blacks. "The opportunity that Hawaii offered – to experience a variety of cultures in a climate of mutual respect – became an integral part of my world view," Obama himself wrote in the 1999 issue of the newsletter published by the elite Punahou School, where he was a pupil from aged 10 until college.

Or as the US representative Neil Hargreaves, a close friend of Obama's parents, more pithily put it while addressing the crowd of 100 supporters here in Kapiolani Park: "Our diversity defines us, rather than divides us."

Obama's attachment to the archipelago survives. His surfing and fish-spearing days may be done, but he spends most Christmases here. If he becomes President, Waikiki could be his Crawford, Texas. (Which would make for a tanned but sadly jet-lagged White House press corps.)

Yet not everything about Obama's formative years here – particularly as one of only a few black students at Punahou, a cradle of academic privilege that led him to a financial scholarship – were glorious. It's maybe why "Obamasada" Bob resists being interviewed in any detail about his memories of the young Obama even though they were friends who loved shooting hoops on the basketball courts on the school campus. "I have been let down by the press," he says, refusing to reveal his last name.

"We've been told not to talk to reporters," volunteers John Cheever, himself an old boy of Punahou and now a sociology teacher there. "He wasn't that much of a distinguished student but everyone will tell you he was a good guy, very popular, someone who was always comfortable with the other kids."

Cheever knows though that there are some not so comfortable memories for Obama from his Punahou years, the kind of stuff that gets the media digging. In searching for the real Barack Obama – or, as they used to call him at school, "Barry O'Bomber" because of his elegant hook shots on the basketball courts – the murk is more likely to be about drugs, including marijuana and cocaine, and slipping grades.

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Over a decade ago, however, Obama did something out of the ordinary. Fresh out of Harvard Law School, he took time off to write a book about his youth – here, in Indonesia and at colleges both in California and in New York. He was not coy. What he revealed in Dreams From My Father about his Punahou years was greeted by many who knew him here with some shock. He wrote about the pain of reconciling the mythology that was spun around his father with the reality that he had been ditched by him, about his struggles of self-identity as a black boy entering a school where one of his first experiences was being asked by another student if his father "ate people". He wrote about the drugs too.

He recalled, for instance, standing in the freezer room of grocery shop with a friend, Micky – "my potential initiator" – and watching as he "pulled out the needle and the tubing" before injecting. Obama described a feeling of panic witnessing this. He did not partake. But there was, before he pulled himself out of it, a period of pot and the cocaine. An entry by Obama in the 1979 school paper, The Ohauan, includes a thank you to the "Choom Gang". "Chooming" in Hawaii means smoking marijuana.

"Junkie. Pothead. That's where I'd been headed: the final fatal role of the young would-be black man. Except the highs hadn't been about that, me trying to prove what a down brother I was. Not by then, anyway. I got high for just the opposite effect, something that could push questions of who I was out of my mind, something that could flatten out the landscapes of my heart, blur the edges of my memory."

There are no plaques to Obama on the Punahou campus or photos of him to celebrate the new-found political prominence of an old boy. At least not yet. Rather, on a small terrace outside the cafeteria there is something which, in a moment of naughtiness, he left behind himself. There scratched into a patch of cement is his name, "OBAMA". Some say another boy scrawled it there because the name seemed funny

But school press officer Laurel Husain, my guide around the stately campus, believes he wrote there himself. Husain, once a Punahou student herself, confirms what others have said: that none of Obama's teachers, many of whom are still teaching, knew of the turmoil he suffered. "They only found out from the reading the book and were surprised. They did not see it. He was outgoing and friendly and well-liked and wasn't someone sticking with cliques." As for the experimenting with drugs as a student there, she points out that the Seventies were a particular time. "It would have been odd if he hadn't."

Lawrence Tavares played with Obama on the school's basketball team, which went on to win the state championships. Now an inheritance planner at the First Bank of Hawaii, he too was taken aback by the book, he confesses. "He just seemed a normal person," he said over the weekend. "We didn't notice much, I guess. At school, he just seemed one of the boys."

A boy, by all accounts, who when not in class dribbled a basketball constantly and went to practise with pals on the courts whenever he had the chance.

Obama was a jock, who, unusually, also cut something of a literary figure on campus. Among poems submitted to the school magazine, one began: "I saw an old forgotten man/On an old, forgotten road". The man, seemingly a reference to his grandfather is "staggering and numb" but finally "pulls out forgotten dignity from under his flaking coat/ And walks a straight line along the crooked world".

But what of the book, published in 1995? Was it wise of Obama to write so candidly of his youthful indiscretions and internal struggles? Maya Soetoro-Ng, his half-sister and 16 years his junior, who has been campaigning for him across the Aloha islands ahead of today's caucus votes, and who also takes the microphone at the park rally, has no doubts. "I think he couldn't be a politician if he couldn't be honest about who is and has been," she said afterwards. "He wouldn't be able to do it. Part of what makes him a leader is his courage. He is glad he wrote it." Words are important to both of them. When they meet they make sure to set aside time for Scrabble, she says.

Obama has also written that the restless ambition that propelled him into the US Senate and his quest for the presidency first struck him after leaving Hawaii, notably while at Columbia University in New York. But Cheever, the teacher, says Punahou may also have had a lot to do with it. "The kids at the school see how others who graduated from it did exceptional things. And they get to think, 'I am kind of not doing anything'." (Graduates include the AOL founder Steven Case and an astronaut.) Meanwhile, the unusual challenges that the young Obama faced, he adds, surely also helped form him.

Cheever, who is wearing a "Buff and Blue for Obama" badge (the colours of Punahou) is talking not just about Obama's struggles over his mixed race but also the shortfalls of his home life. His father had vanished and his mother, Ann, was still mostly absent, leaving her parents, Stanley and Madelyn, to raise her son in their small Honolulu apartment while she remained in Indonesia. Madelyn still lives in the home, though at 84 years old is frail and has refused all interviews. "Having a single mother and being raised by your grandparents, that has to give a certain resiliency, the power to overcome," he suggests.

But then there were the influences of his parents themselves. Few knew them as well as Neil Abercrombie, who, in particular, has memories of Obama's father, also named Barack, that go much beyond the shorthand of his once being a goatherd in his native Kenya. He came to study in Hawaii after being singled out to help Kenya shed its colonial past. At university that he met Ann. (Ann, who died of cancer in 1995, was actually named Stanley, because of the disappointment of her father – Gramps to Barack – at having had a girl instead of a boy. Naturally she preferred Ann.)

"His father was truly a force of nature and a brilliant intellectual," Abercrombie offers. "The intellectual apple didn't fall far from the tree." Just as his father was sometimes fiery, so his mother, Ann, he added, was calm and contemplative. "He has the voice of his mother."

But Abercrombie, like so many of his supporters here, soon returns to the multicultural, multi-ethnic influences of the islands of his teenage years and the lessons of tolerance they taught him. "The culture of Hawaii, the values of Hawaii, these are things that shaped the foundations of his life."

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