I have a fantasy. It’s that every politician and pundit who goes on TV to discuss the Iran deal is asked this question first: “Did you support the Iraq War, and how has that experience informed your position?”

For me, it would be a painful question. I supported the Iraq War enthusiastically. I supported it because my formative foreign-policy experiences had been the Gulf War and the wars in Bosnia and Kosovo, all of which led me to exaggerate the efficacy of military force and downplay its risks. As Iraq spiraled into disaster, I felt intellectually unmoored. When my sister-in-law was deployed there for a year, leaving her young daughter behind, I was consumed with guilt that I had contributed to their hardship. To this day, when I walk down the street and see a homeless veteran, I feel nauseous. I give some money and a word of thanks, and think about offering an apology. But I don’t, because there’s no apology big enough. The best I can do is learn from my mistake. These days, that means supporting the diplomatic deal with Iran.