Linda Bilmes, a Harvard expert on financing war, told me that most of the costs will arrive later. For example, any soldier who develops a medical disorder or aggravates an existing one will receive lifelong benefits and medical care. If today’s troops claim such benefits at the same rate as those who participated in the 1990-91 gulf war, that alone would eventually cost at least $600 billion, Bilmes said. Not to mention, of course, the human toll of all of this.