Newswise — George W. Bush’s decision to invade Iraq following the terrorist attacks of Sept. 11, 2001, arguably was the most important decision of his presidency.

That momentous decision also is central to understanding the psychological makeup of one of the most polarizing figures in American history, according to a new book by Dan McAdams, chair and professor of psychology in the Weinberg College of Arts and Sciences at Northwestern University. McAdams, who read everything he could about Bush every morning for a year, set out to write a serious psychological analysis that steers a middle course between the slew of books by admirers who love everything the 43rd president did and detractors who demonized him and his policies.

“George W. Bush and the Redemptive Dream: A Psychological Portrait” (Oxford University Press, 2010) has just been released.

McAdams looks at Bush through the prism of a personality framework that he has developed over the past 25 years, concluding that the president’s bold decision to invade Iraq was greatly influenced by a distinctive combination of Bush’s personality traits, family goals and a story of redemption that he crafted for his own life.

The likelihood is not great that other men or women who might have held that office would have made the same decision about Iraq, McAdams concluded. Bush’s unique personality was key.

McAdams went back in time to get the full picture of Bush’s life before seizing upon the Iraq decision as the focus of his book.

“Other factors, of course, could explain the decision -- factors that have to do with politics and world events and geo-strategic kinds of considerations,” McAdams said. “But you can’t discount the psychology factor.

“We know, for example, that his father when he was president did not decide to launch an invasion of Iraq to upend Saddam (Hussein) -- even when he had the opportunity to do so.”

Below McAdams discusses his new book with Hilary Hurd Anyaso, law and social sciences editor at Northwestern.

Please explain your personality framework.

In essence, the framework suggests that a foundational layer of dispositional traits begins to emerge early on in life; a second layer of goals and values starts to form in middle childhood; and a third layer of an internalized story that we create about our lives starts to play out in young adulthood. A person’s story is layered over his or her own goals and values, which are layered over basic dispositional traits. The story is strongly shaped by culture; the goals develop in our families, schools and other social settings; and the traits are strongly driven by genetic tendencies.

Which of the three layers of personality are the most revealing about Bush?

Each of the three layers of personality reveal interesting aspects of Bush – and all had an impact on the Iraq decision.

Evident even in early childhood, his basic traits of sky-high extraversion and rock-bottom openness to experience set him up to act in a bold and decisive way in response to life’s challenges. He was, therefore, psychologically primed to do something like an Iraq invasion. Sept. 11 created an environment that favored the kind of response that a person with Bush’s basic traits was psychologically prepared to make. The traits tell you how a person will act in general, basic behavioral style. But to know exactly what he or she will do, you need to look at the second layer of personality.

When you go to the (second) layer of goals in a person’s life, you look at what people want, what are they trying to obtain. In George W.’s case, a major goal throughout his life was to defend his beloved father against his worst enemies. He was devoted to his father as the first-born son. After the 9/11 attacks, he got this wonderful opportunity, psychologically speaking, to fulfill this deep goal -- to kill off his father’s greatest enemy, Saddam Hussein. It is nearly impossible to overestimate George W.’s deep and personal hatred for Saddam.

Most important for understanding Bush is the third level of personality, which is the story we create for ourselves to give our lives a sense of meaning and purpose.

George W.’s story was a classic American story of redemption. It was a story he began to create for himself in his middle adult years around the age of 40 after he had overcome many adversities in his life -- most of them self-imposed. After many years of drinking and revelry and squandering his 20s and 30s, he managed through marriage, through a religious conversion and through giving up alcohol to turn his life around. He made his story about a prodigal son who comes home and redeems his life and makes it better. Through self-discipline and God’s help, Bush restored his lost sobriety, freedom and goodness.

His redemptive story gives focus and meaning to his own life, and after 9/11, he projects this same story onto us – the world. In the same way that he had overcome the chaos in his own life to restore goodness, so too could America, with self-discipline and God’s blessing, regain her greatness by fighting the good fight against a terrible tyrant – who happened to be his father’s greatest enemy.

What most influenced Bush as a person, and subsequently, a president?

Finding Laura was a stroke of tremendous genius. Had he met her 10 years before, nothing would have happened. She was a real adult, and at 31 George finally was ready to be an adult. The birth of their twins in 1981, Jenna and Barbara, after a period of infertility, also was a big deal. Third is the religious conversion, and the last and culminating moment was giving up drinking around his 40th birthday.

Are there particular personality traits that he shares with past presidents?

In fact, a group of psychologists and historians have rated all the presidents, going back to George Washington, in terms of the five basic traits of personality -- extraversion, neuroticism, agreeableness, conscientiousness and openness to experience. Two were key for Bush. Extraversion is about how socially dominant, gregarious you are. Openness to experience gets at how imaginative you are, how much you seek novelty and change.

Bush was near the top of extraversion and at the bottom of openness to experience.

Presidents who tend to be rated low on openness to experience are often seen as very clear-minded men of conviction who don’t change their minds very much. Bush was set in what he believed. He lost very little sleep after the decision to invade Iraq.

Under the best of circumstances, a person with those two traits moves through life with tremendous social energy, confidence and social dominance. On the down side, this trait profile can make for impulsive actions and an unwillingness to perceive the world from others’ points of view. Thus, Bush has a tendency to make bold decisions, to not question himself. There’s a confidence here that borders on hubris and a lack of interest in seeing the world the way other people see it.