One of the downsides of being president of the United States is that anything you wrote as you were growing up, whether inane or intimate, will someday be dusted for clues. In David Maraniss' massive biography of the young Barack Obama, we get to hear the future president's voice in a high school classmate's yearbook:

Tony, man, ... been great knowing you and I hope we keep in touch. Good luck in everything you do, and get that law degree. Some day when I am an all-pro basketballer, and I want to sue my team for more money, I'll call on you.

If Obama ever had a sense of destiny, he wore it lightly. "Barack Obama: The Story" underscores the fact that few U.S. presidents have followed such an improbable course.

Not only was his family without money or connections, he grew up in a broken home half a world away from the nation's power centers. He was a mixed-race kid who looked black, felt white and spent much of his early life struggling to reconcile the two.

As with his 1995 study of Bill Clinton's early life, "First in His Class," Maraniss, a Washington Post journalist, didn't wait for the end of the Obama presidency to piece together his life. His groundbreaking work and exhaustive research ensure that "The Story" is the volume that future Obama biographers reach for first.

In James Michener-like fashion, Maraniss goes around the world and several generations back to tell the stories of Obama's Kansan and Kenyan forebears and how the clans met in 1960, in the persons of charismatic Barack Obama of Nairobi and bookish Stanley Ann Dunham of Seattle, in a Russian class at the University of Hawaii.

Their baby was born 10 months later -- and 165 pages into the book.

Maraniss takes Obama through his college years at Occidental and Columbia, a stint at a New York corporate newsletter firm and a short career as a Chicago community organizer. The book ends with him entering Harvard Law School at 27, in hopes of learning to work the levers of power.

The theme of Obama's early life, Maraniss says, was his ongoing effort "to avoid life's traps" -- not allowing himself to be defined or circumscribed by his unusual family history, his rearing or his race. To do that he became uncommonly cautious and analytical, more an observer than an actor.

The Maraniss book serves as a historical corrective for Obama's 1995 memoir, "Dreams From My Father," which the author said compressed people and events and wasn't meant to be strictly factual. For instance, Obama's book says his family broke up when his father left Hawaii in 1963; Maraniss finds that Dunham actually moved the baby to Seattle within a month of his birth in August 1961.

While the book raises questions about some of Obama's choices, it won't appeal to those looking for conspiracies. Maraniss finds that Obama's Kenyan family was far more influenced by Christians than Muslims. For birthers, Maraniss reports a memorable conversation between a doctor and a journalist shortly after Obama was born that again confirms it happened, yes, in Honolulu.

By 1988, when he leaves Chicago for Harvard in a yellow Datsun with a hole in the floorboard, Obama has found a home and an identity and -- whether he knows it or not -- a path that will lead to the White House. After reading Maraniss, one suspects that by then he had an inkling.

Kevin Duchschere is a reporter for the Star Tribune.