[I]t is a profound and painful thing to accept that one’s country has involved itself in a futile or immoral cause; it is worse still to ask what intellectual or political mistakes led to such a nightmare. Faced with a disastrous war, the most important consideration is not “Were we wrong?” but “Why were we wrong?” and “How can we avoid being so wrong in the future?” These are questions that often will implicate the country’s leading politicians and intellectuals, and its cherished myths. The anguish of confronting them has been on display in the Democratic Party’s foreign policy debate for 35 years. … It is only when the United States shrinks from asking such agonizing questions that we wade back into agonizing wars.