To read Sally H. Jacobs’s new biography of Barack Hussein Obama Sr. is to realize that his son, the president, spent much of his life reaching for a shadow he was lucky never to catch. Early in The Other Barack, a childhood playmate recalls how Obama Sr. would frequently snap at him and shout, “You don’t know what you are talking about.” A few chapters later, the editor of the University of Hawaii literary magazine describes Obama Sr. barreling into his office, unprovoked, to declare that a particular poem wasn’t “worth a damn.” Back in Nairobi, says one government official, Obama Sr. would “slam his fist on the table” and claim that a rival “knows nothing about math or economics”; he would go on to describe other colleagues as “intellectual dwarfs.” As college friend and current Hawaii Gov. Neil Abercrombie tells Jacobs, Obama Sr. could never “contain his irritation with people who were not as facile as he, and he did not hesitate to say so.”

The president, of course, has a healthy ego. But this is something else. Every shred of available evidence—which Jacobs, a veteran reporter, spent two years and 75,000 miles of intercontinental travel ably assembling—suggests that the senior Obama was an unmitigated jerk: a coxcombish souse who forced friends to cover his abundant bar tabs and repeatedly broke his legs in boozy car crashes; an uncooperative contrarian who was promptly fired from, or sidelined at, every job he ever had; a compulsive philanderer who ditched his first wife, Kezia Nyandega, when he moved to America, abandoned the president’s mother, Ann Dunham, when he left Hawaii for Harvard, and lured his third wife, Ruth Baker, to Kenya only to beat, berate, and cheat on her.

And yet, if Obama Sr. were only a jerk, there wouldn’t be any reason to read about him, regardless of who his son turned out to be. But there is. Like the president, Obama Sr. was also a brilliant, ambitious idealist who overcame the limited circumstances of his background to attend the best schools in the world, then set out to participate in a moment of vast political promise. That he failed so spectacularly, and that his son succeeded, says a lot about the qualities of character that can distinguish a leader from a lout.

The elder Obama’s biggest problem was his desperate need to dominate everyone he encountered—the result, according to Baker, of “a great, enormous insecurity.” As a child in rural Kenya, Obama Sr. cobbled together the best education he could; when he was denied a spot on the famous 1959 East African student airlift, he made his own way to America. In Hawaii, and later at Harvard, where he studied for a Ph.D. in economics, he was determined to amass the kind of mathematical expertise that would earn him a place in Kenya’s new ruling class—the young, largely foreign-educated elite destined to shape the country’s postcolonial future. But when Harvard’s WASPy authorities got wind of Obama Sr.’s womanizing, they revoked his scholarship and forced him to return to Kenya before he could complete his dissertation. He never got his degree. Instead, he spent the next few years swanning around Nairobi in a blue Ford Fairlane, insisting that people address him as “doctor,” and earning the nickname Double-Double by downing successive twin shots of Johnnie Walker Black—all while alienating potential allies and benefactors with constant (and increasingly drunken) complaints about how much smarter he was than the rest of humanity. “He pretended to be this great fellow, but we all know that confident people do not have to blow their horn like that,” Baker tells Jacobs. “Nor do they have to drink all the time to give themselves false confidence.”

Despite his obvious intelligence and ample charm, Obama Sr. never developed the institutional finesse required to secure a position of power or put his policy proposals into practice. He was too busy overcompensating for his insecurities and stepping on influential toes. In late 1964, he turned down a government planning job because the pay was “peanuts” and the man slated to share his title “kn[ew] nothing.” His counterpart went on to become one of Kenya’s most prominent political and business leaders. A few months later, the newly independent government released a paper outlining its economic philosophy: vigorous growth fueled by a free-market economy and foreign investment. Although the country’s leftists objected, few risked reprisal by speaking out. But Obama Sr. boldly published a counterproposal. It was, in Jacobs’s words, “a creative blending of the opposing economic principles that were under debate.” Unfortunately, it also included “a provocative shot” at the autocratic president and “threw a shadow over” his relationship with the paper’s author, a former benefactor. “I pleaded with him to be moderate in what he said,” Kenyan politician Peter Aringo tells Jacobs. “But he would not.” In mid-1966, a sloshed Obama Sr., now something of an outcast, slammed his friend Adede Abiero’s Fiat into another vehicle, killing the 26-year-old Abiero, who was riding shotgun.

Although his broken bones would heal, Obama Sr. never really recovered. The loud, late-night fights with Ruth, lonely and thousands of miles from home, became more frequent and more violent; eventually she left, and the gifted Harvard student she’d fallen in love with faded into a fog of chauvinistic carousing. Now a senior tourism officer, Obama Sr. began to impersonate his superiors while on assignment; he was fired after less than three years on the job. He soon lost his house and started sleeping on friends’ sofas. After surviving yet another car crash, he told one acquaintance, “Well, you see, now even God does not want me.” A trip to Honolulu was awkward for everyone, including 10-year-old Barack, who “count[ed] the days until my father would leave.” In 1975, Obama Sr. secured his final job: a menial finance position usually reserved for recent college grads. Previously, “he had been assigned to help run an institution,” Obama Sr.’s boss tells Jacobs, “but his personality quite frankly was not up to it.” In 1982, he drove into a tree stump and died on impact.

Jacobs doesn’t dwell on the differences between Obama Sr. and his son, but reading her book, one can’t help but conclude that the younger Barack has matured, for whatever reason, into a near-perfect negative image of the elder: formed from the same template and yet precisely opposite in every cast and contour of his character. Unlike his father, the president is a committed family man who rarely drinks, who never loses his cool, who values pragmatism over idealism, who prefers consensus to conflict, and who has mastered the art of working within the system. To say that Obama’s personality—compulsively rational and almost supernaturally controlled—is the only source of his success would be reductive. It would also be simplistic to suggest that his temperament is somehow a reaction to the excesses of a father he never really knew. Still, the tragic story of The Other Barack throws into sharp relief the traits that make America’s current president so exceptional. The audacity of hope is all well and good, but it takes more to change the world.