I thought this paragraph from the conclusion of The Threatening Storm was worth posting in full:

The best way to think about sorting out the priorities between Iraq and al-Qa’eda is to imagine that the United States invades Iraq and that while we are doing so, al-Qa’eda conducts another terrorist attack that results in the death of several hundred Americans. In this hypothetical scenario, the president should be able to honestly tell the relatives of the victims killed that there was nothing else the US government could have done to prevent the attack and there was nothing about the operations in Iraq that distracted or diminished the nation’s vigilence against al-Qa’eda. Only when the administration can meet this standard should we embark on so large an additional endeavor as invading Iraq.