While serving as President Gerald R. Ford’s chief of staff in the mid-1970s, Donald Rumsfeld started keeping a list of rules and favorite sayings. They included “don’t stay on the job too long,” “if you foul up, tell the president and others fast, and correct it,” “don’t speak ill of another member of the administration,” “read and listen for what is missing” and keep other staff members in the loop because “if they are out of the flow of information, decisions will either be poorly made or not made — each is dangerous.”

During his tenure as secretary of defense under George W. Bush, Mr. Rumsfeld would violate most of these rules. And as Bradley Graham, a former military and foreign affairs reporter for The Washington Post, observes in his conscientious new biography, the SecDef’s mismanagement of the wars in Iraq and Afghanistan would make him, in the eyes of many critics, the very “personification of the arrogance and misjudgments of the Bush administration,” from its embrace of idées fixes and impatience with dissenting viewpoints, to its debilitating interagency turf wars, to its inability to admit mistakes or change direction.

In “By His Own Rules,” Mr. Graham goes out of his way to give Mr. Rumsfeld the benefit of the doubt. Where some reporters and former administration insiders saw the defense secretary’s eagerness, in the immediate aftermath of 9/11, to move the battlefield to Iraq as a reflection of “his desire to see U.S. troops in the lead someplace rather than playing a supporting role to the C.I.A. in Afghanistan” (for which the Pentagon had no real plan), Mr. Graham writes that contemporaneous “accounts of internal Pentagon discussions and memos” simply “suggest that Rumsfeld was motivated by an aggressive view of how to proceed.”