If success has a thousand fathers and failure is an orphan, it is no wonder that the number of intellectuals willing to endorse the Iraq war is shrinking fast. For the small but significant camp of pro-war liberals, the decision to support the American invasion of Iraq was always deeply conflicted, a matter of weighing security concerns and humanitarian promise against the dangers of unilateralism and militarism. The war, for them, presented a classic example of what philosophers call “moral luck,” a decision whose morality cannot be evaluated in advance: Only success would make the war justifiable, not just pragmatically but ethically. And as peace and democracy in Iraq have proved as elusive as Saddam Hussein’s WMDs, liberals like David Rieff and George Packer have written with genuine anguish about their willingness to support the use of force for liberal goals. As Alan Dershowitz points out in his new book, “Preemption,” one of the most significant casualties of the Iraq War may be America’s ability to achieve political consensus on military responses to future threats.

For a pro-war liberal to turn against the Iraq war, however, while it may be wrenching, is not really surprising. The real man-bites-dog story comes when a self-proclaimed neoconservative, a genuine Middle East hawk, decides that the war was a mistake. That is why Francis Fukuyama’s recent New York Times Magazine essay, “After Neoconservatism,” created such a stir. Mr. Fukuyama, after all, has long been one of the most prominent neoconservative policy intellectuals. As he writes in “America at the Crossroads” (Yale University Press, 240 pages, $25), the new book from which his essay was excerpted, he has worked or studied with most of the leading neoconservatives, both in and out of government: Paul Wolfowitz, Allan Bloom, William Kristol, Albert Wohlstetter. Most important, he is the author of “The End of History and the Last Man,” a book both celebrated and reviled as the classic neoconservative verdict on the Cold War.

Yet Mr. Fukuyama now believes that the Iraq war was a mistake, and that his neoconservative comrades have permanently discredited that label. “Unlike many other neoconservatives,” he declares at the outset of his new book, “I was never persuaded of the rationale for the Iraq war.” And now that events have borne out his fears,Mr. Fukuyama has “concluded that neoconservatism, as both a political symbol and a body of thought, has evolved into something I can no longer support.” The titular crossroads at which America stands, he goes on to argue, is the choice between continuing the failures of actually existing neoconservatism – its overestimation of America’s power and credibility, its naivete about the difficulties of spreading democracy – and Mr. Fukuyama’s more hardheaded alternative, which he names “realistic Wilsonianism.”

The further one reads in Mr. Fukuyama’s thoughtful book, however, the more subtle his apostasy starts to appear. A realistic Wilsonian, in Mr. Fukuyama’s telling, looks very much like a neoconservative who has been mugged by reality – and who understands that the label has attracted so much political abuse that it will no longer serve as a standard to march under. In fact, despite the dramatic headline “After Neoconservatism,” Mr. Fukuyama’s recent career by no means suggests a break with his past positions; he seems committed to reforming his comrades, rather than abandoning them. Just last year, he helped to start a new magazine, the American Interest, which is fundamentally neoconservative in orientation, after the original journal of neoconservative foreign policy, the National Interest, was taken over by new owners whom Mr. Fukuyama deemed unacceptably “realist.”

Even his opposition to the Iraq war is a more complicated story than he suggests in “America at the Crossroads.” In his preface, he acknowledges having signed a 1999 open letter from the Project for a New American Century calling for a tougher stance on Saddam. What he oddly fails to mention is that, in fact, he signed an even stronger letter just after September 11,2001,which declared that “any strategy aiming at the eradication of terrorism and its sponsors must include a determined effort to remove Saddam Hussein from power in Iraq. Failure to undertake such an effort will constitute an early and perhaps decisive surrender in the war on international terrorism.” The question “America at the Crossroads” has to answer is what changed between 2001 and 2006 to make Mr. Fukuyama stop believing that the removal of Saddam from power was in America’s vital interest.

The answer, however, never becomes completely clear. Mr. Fukuyama’s chief objections to the administration’s handling of the Iraq war are that the WMD threat turned out to be less acute than suspected, and that the postwar occupation was damaged by deeply inadequate planning and troop commitment. But these are both ex-post-facto objections: They could not necessarily have been foreseen before the invasion took place. In other words, Mr. Fukuyama raises the old problem of moral luck: If things had turned out differently in Iraq, he would not now be objecting to the decision to invade. What troubles Mr. Fukuyama is not the principle behind the invasion, but its execution. He holds America responsible not for a crime, as the most determined anti-war polemicists would have it, but for a mistake.

That distinction is crucial to understanding Mr. Fukuyama’s prescription for the future of American foreign policy. Early in the book, in the course of a lucid and sensible discussion of the intellectual origins of neoconservatism, Mr. Fukuyama lists four principles that he regards as essential to the movement, each of which distinguishes it from a competing school of foreign policy thought. Unlike Kissingerian realists, neoconservatives hold “a belief that the internal character of regimes matters and that foreign policy must reflect the deepest values of liberal democratic societies.” Unlike isolationists, they believe “that American power has been and could be used for moral purposes, and that the United States needs to remain engaged in international affairs.” Unlike the left, they have “a distrust of ambitious social engineering projects.” And unlike liberal internationalists, they retain “skepticism about the legitimacy and effectiveness of international law and institutions to achieve either security or justice.”

In the course of his short book, which touches on foreign-policy matters large (the frustrations of Third World development) and small (the system for assigning Internet domain names), Mr. Fukuyama never really repudiates any of those neoconservative beliefs. Instead, “America at the Crossroads” reads more like a tactical retreat, an acknowledgement that neoconservative goals need to be carried out through more thoughtful, modest, and multilateral means. Mr. Fukuyama calls for less emphasis on military power and more on democracy promotion and consensus-building – a prescription that is hard to argue with. But as even he acknowledges, “preventive war and regime change via military intervention can never be taken off the table completely.” America’s next tough decision – for instance, how to respond to the threat of a nuclear Iran – will show whether Mr. Fukuyama’s “realistic Wilsonianism” is a distinctively new approach to foreign policy, or just neoconservatism with a human face.