As the war in Iraq drags on, and more and more is learned about the missteps and misrepresentations made in the walkup to the war, it becomes clear that former Secretary of State Colin L. Powell — who harbored serious doubts about the wisdom of invasion and who frequently found himself an outsider in an administration dominated by neo-conservative hawks — was prescient about a host of issues, from the difficulties of rebuilding a postwar Iraq to the need for higher troop levels and multilateral support.

Even as his foresight is underscored, journalists and former colleagues have continued to ask: Why didn’t Mr. Powell resign when he realized that much of his advice was being ignored? Why didn’t he more forcefully express his reservations about the war to President Bush? Why did he put up with being cut out of major foreign policy decisions by Vice President Dick Cheney and Defense Secretary Donald H. Rumsfeld? Why was he unable to make the president and the Pentagon heed the tenets of the “Powell Doctrine” (which held that military commitments must be made with decisive force, a clear objective and popular support, to avoid another Vietnam)?

As Karen DeYoung, an associate editor of The Washington Post, notes in her new biography, various theories have been advanced to explain Mr. Powell’s decision to quietly stick out his first-term tenure as secretary of state. She writes that some of his closest overseas counterparts speculated “that his military background made him unwilling to question orders or that any black man who reached the top in America must have done so by toeing the line.”

She observes that some Foreign Service officers believed that he stayed put because he was “the only thing standing between a sustainable foreign policy and utter national disaster,” and that in the words of one assistant secretary, he prevented “much worse stuff from happening.”

And, finally, she suggests that Mr. Powell let the administration use his prestige and popularity “even as it repeatedly undermined him and disregarded his advice,” at least in part because he “simply refused to acknowledge the extent of the losses he had suffered”: “Beyond his soldier’s sense of duty, he saw even the threat of resignation as an acknowledgment of defeat. He was a proud man, and he would never have let them see him sweat.”