When I served in the George W. Bush White House, I believed before the war began that it was justified — that Saddam Hussein possessed weapons of mass destruction, that he was a particularly malevolent and destabilizing figure, and that it was a military conflict that would liberate an enslaved people.

These presuppositions caused me to ignore, much longer than I should have, the problems inherent in our occupation strategy. I didn’t question early enough the errors we made or how the situation was unraveling.

I recall a lunch in early 2006 with a journalist, George Packer, who had just returned from Iraq. A colleague and I, already worried about the course of the war, wanted to hear his firsthand account. What he described was so troubling that my head nearly dropped into my food. In ways I had not fully understood at the time, I had been filtering out information that ran counter to the narrative I believed.