With the Vietnam War raging, 21-year-old George W. Bush wanted to join the Texas Air National Guard in 1968. He offered no aviation experience but cited his work as a ranch hand, oil field "roustabout" and sporting goods salesman. He passed the written test required for pilot trainees. Among the results: He showed below-average potential as a would-be flier but scored high as a future leader. Although Mr. Bush's unit in Texas had a waiting list for many spots, he was accepted because he was one of a handful of applicants willing and qualified to spend more than a year...