The surest proof that the Iraq War ended in disappointment and failure is that it has receded into history as an orphan: “George W. Bush’s war,” as it came to be known. As we mark its 20th anniversary, the gradual narrowing of responsibility has become one of several key myths with which we should dispense once and for all. One might be forgiven for assuming that the terrible misfortunes of the Iraq War came by way of a hitherto-obscure faction of neoconservatives. The culpability of this faction has become a dogma of the progressive Left as much as it has of the post-Trump Right. In this telling, the good and great American people were little more than bystanders to the ruinous idealism that sought to export democracy at the point of a gun. After emerging morally untainted, they have been justly chastened about the limits and the iniquities of American power ever since. This storyline obscured a salient truth about the war that has since been all but forgotten: namely, that it had been a national enterprise. Before U.S. soldiers took the field, a broad array of America’s political leaders, including every subsequent presidential nominee of each party who had been in Congress at the time of the war, blessed this campaign in the Arab world. Rightly or wrongly, the war proceeded from all-too-common assumptions that had informed successive administrations and that had been endorsed...