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,...