At the pentagon on the afternoon of 9/11, as the fires still burned and ambulances blared, Secretary of Defense Donald Rumsfeld returned from the smoke-filled courtyard to his office. His closest aide, Undersecretary Stephen Cambone, cryptically recorded the secretary’s thinking about Saddam Hussein and Osama (or Usama) bin Laden: “Hit S. H. @same time; Not only UBL; near term target needs—go massive—sweep it all up—need to do so to hit anything useful.”

The president did not agree. That night, when George W. Bush returned to Washington, his main concern was reassuring the nation, relieving its suffering, and inspiring hope. Informed that al-Qaeda was most likely responsible for the attack, he did not focus on Iraq. The next day, at meetings of the National Security Council, Rumsfeld and Deputy Secretary of Defense Paul Wolfowitz advocated action against Saddam Hussein. With no good targets in Afghanistan and no war plans to dislodge the Taliban, Defense officials thought Iraq might offer the best opportunity to demonstrate American resolve and resilience. Their arguments did not resonate with anyone present.

The following evening, however, President Bush encountered his outgoing counterterrorism expert, Richard Clarke, and several other aides outside the Situation Room in the White House. According to Clarke, the president said, “I want you, as soon as you can, to go back over everything, everything. See if Saddam did this. See if he’s linked in any way.” Clarke promised he would but insisted that al-Qaeda, not Hussein, was responsible. Then he muttered to his assistants, “Wolfowitz got to him.”

There is no real evidence that Wolfowitz did get to Bush. The president may have talked about attacking Iraq in a conversation with British Prime Minister Tony Blair on Friday, September 14. But when Wolfowitz raised the issue again at Camp David over the weekend, Bush made it clear that he did not think Hussein was linked to 9/11, and that Afghanistan was priority No. 1. His vice president, national security advisers, and CIA director were all in agreement.

Bush’s decision to invade Iraq was neither preconceived nor inevitable. It wasn’t about democracy, and it wasn’t about oil. It wasn’t about rectifying the decision of 1991, when the United States failed to overthrow Hussein, nor was it about getting even for the dictator’s attempt to assassinate Bush’s father, George H. W. Bush, in 1993. Rather, Bush and his advisers were motivated by their concerns with U.S. security. They urgently wanted to thwart any other possible attack on Americans, and they were determined to foreclose Hussein’s ability to use weapons of mass destruction to check the future exercise of American power in the Middle East.

Bush resolved to invade Iraq only after many months of high anxiety, a period in which hard-working, if overzealous, officials tried to parse intelligence that was incomplete and unreliable. Their excessive fear of Iraq was matched by an excessive preoccupation with American power. And they were unnerved, after 9/11’s shocking revelation of an unimagined vulnerability, by a sense that the nation’s credibility was eroding.