The book works to the extent it does because the people doing the talking carry weighty credentials. Zbigniew Brzezinski was National Security AdvisOr to President Jimmy Carter from 1977 to 1981, and Brent Scowcroft did the same job for Gerald Ford from 1974 to 1976, and again for George Bush Sr from 1988 to 1992. Before and after their stints in the West Wing, both men spent decades near the centre of the small, tight-knit, fiercely competitive group which shaped America’s foreign and strategic policy in the years after Vietnam. They were both therefore central players in the Cold War, and among the architects of America’s victory in that strange struggle for global primacy. They come from different sides of American politics – Brzezinski is a Democrat, Scowcroft a Republican – but their conversations in this book convey a profound consensus about America’s purposes in the world and how they can best be served. They disagree occasionally about tactics but agree on all the big issues, and on those they echo the values and approaches that, they believe, won the Cold War: realism, prudence and steadiness, and a firm grasp of history.

 Not surprisingly, then, neither Brzezinski nor Scowcroft has anything nice to say about the forty-third president. Throughout their book, both men roundly criticise the policies of the Bush administration. They are not latecomers to this view; both men opposed the Iraq War from the start. Now they urge the next president to avoid Bush’s mistakes, and offer sensible-sounding suggestions about many of the key problems that Obama will face in his first months in office: how and when to withdraw from Iraq, how to win in Afghanistan, how to deal with China, how to manage Russia. They want less bluster and more firmness, less posturing and more negotiation, less lecturing and more listening.

It is hard to disagree with any of this. And yet there is a pervasive sense that this book does not quite get to the nub of things. As each conversation unfolds, the speakers make sensible points but duck the hard choices. They say America should talk to Tehran, but they do not say whether it could live with a nuclear-armed Iran, and whether it can, in the end, do anything to prevent it. They say America should encourage a settlement between the Israelis and Palestinians, but not what it should do to bring the two sides to accept the deal which everyone knows is there to be made. They say America should work with a rising China to bring it peacefully into the international system, but they do not say whether it is willing to make room for China’s aspirations to leadership as its power approaches America’s own. They do not say whether America should be willing to treat China as an equal, nor whether they expect China to settle for anything less.

There is a pattern to these evasions. While they repudiate Bush’s methods, Brzezinski and Scowcroft essentially share his aims. They share his unquestioned belief that the only possible purpose for American foreign policy is to consolidate and extend American global primacy. But they shy away from explaining how those broad purposes can be achieved with the power America can command today and over the next few decades. Instead they look back, evoking a time when America’s fortunes were guided by wise men, like themselves, who eschewed the populism and bitter partisanship that led America astray during the Bush years. To their credit, Brzezinski and Scowcroft themselves take occasional aim at this nostalgic image. And yet their book’s key message is that America’s power and standing in the world will be restored simply by putting the mistakes and misdeeds of the Bush era behind it, and returning to the nobler and wiser habits of the past.

This blames George W. Bush for too much. Bad though he has been, there are deeper causes of America’s current foreign-policy problems, from Iraq and Iran, to Russia and China. They stem from a fundamental mismatch between power and purpose: between the nature and scale of American power and the goal of American global primacy over coming decades. America was never as omnipotent after the Cold War as many people, in America and elsewhere, believed. And its relative power is in long-term decline as other countries, especially China, rise. Today’s economic crisis only accelerates a process which seems likely to see China overtake the United States to become the world’s largest economy within a few decades. That already has serious implications for the way the world works. In particular, it has profound consequences for America’s place in the world. Without the essential foundation of economic primacy, it is hard to see how America’s goal to perpetuate its political and strategic primacy can be achieved.

This basic disjunction between America’s power and its purposes underlies the failure of the Bush presidency, but it equally pervades the measured, patrician observations of Brzezinski and Scowcroft. The real questions for US foreign policy are therefore not the ones they discuss in these conversations: questions about how America can rebuild rogue states, transform turbulent regions, forbid the spread of nuclear weapons and preserve unchallengeable global primacy. The real questions are about how America should conduct itself in a world in which it cannot rebuild places like Afghanistan and Pakistan to suit its own interests; in which it cannot transform the Middle East into a haven of pro-Western democracy; in which it cannot prevent countries such as Iran and North Korea building nuclear weapons; in which it cannot prevent Russia enforcing a sphere of influence along its borders; and in which it cannot preserve unchallenged global primacy.

Its failure to recognise the real and growing limits to American power, and the consequences that follow for American aims and purposes in the world, constitutes the real weakness of this book. More importantly, this failing can also be found in Obama’s approach to foreign policy. During the campaign, Obama repudiated the style and tactics of the Bush era, but he too did not reject its objectives and purposes. How could he, when those purposes form an article of faith among the vast majority of American voters, and for that matter of the foreign policy élites? Such positioning was probably essential to set his candidacy up for success, but it risks setting up his presidency for failure. Or perhaps we can look at it more positively, and say that it clarifies Obama’s challenge as president. He needs to close the gap between America’s grand goals and the reality of American power.

So Obama must do more than repudiate Bush’s style; he must challenge and transform Americans’ long-standing, deeply held bipartisan consensus about their country’s place in the world, to bring it into line with the realities of shifting power. That is tough, especially for a Democrat. The logic of politics will push Obama the other way, to prove his national security credentials by sticking to all but the most egregious positions that Bush has marked out. While he closes Guantanamo and runs down in Iraq, he will not want to step back on Iran, North Korea, Russia or China, for fear of being seen as soft. After all, the mid-term elections are only two years away. However, America is a remarkable place. It can reinvent itself, and it has done so in electing Obama. Perhaps it can do so again, and perhaps Obama is the leader to show them the way. Alas, this book won’t be much help.