Israeli soldiers prevent Palestinian worshippers from entering Jerusalem on the first day of Ramadan, at a checkpoint in Bethlehem. (Maan Images)

Given the reception John Mearsheimer and Stephen Walt received for their London Review of Books essay last year on what they called the Israel Lobby, it would have been understandable had they crawled away to a dark corner of their respective academic institutions to lick their wounds. Their argument that US foreign policy has been distorted by the stultifying power of pro-Israeli groups and individuals was met with a firestorm of protest that has smouldered ever since.

The authors were assailed with headlines such as the Washington Post's: "Yes, it's anti-semitic." The neocon pundit William Kristol accused them in the Wall Street Journal of "anti-Judaism" while the New York Sun linked them with the white supremacist David Duke.

The row became a focal point of a much wider debate about the limits of permitted criticism of the state of Israel and its American-based supporters that has ensnared several academics and writers, including a former president. Jimmy Carter was castigated earlier this year when he published a plea for a renewed engagement in the Middle-East peace process under the admittedly provocative title, Palestine: Peace Not Apartheid. He was labelled an anti-semitic "Jew hater" and even a Nazi sympathiser. Meanwhile, a British-born historian at New York University, Tony Judt, has been warned off or disinvited from four academic events in the past year. On one occasion, he was asked to promise not to mention Israel in a speech on the Holocaust. He refused.

For Walt, the explosion of criticism after the LRB publication in March 2006 struck particularly close to home as two members of his own Harvard faculty turned on him. Ruth Wisse, professor of Yiddish literature, compared Walt and his University of Chicago co-author's work to that of a notorious 19th-century German anti-semite. Alan Dershowitz, the Harvard criminal law professor who represented OJ Simpson, charged them with culling some of their references from neo-Nazi websites.

Given the battering he has taken, Walt is remarkably upbeat. "We were surprised by how nasty it got," says the Harvard professor. "The David Duke reference, the neo-Nazi websites - these were intended to smear us and swing attention on to us rather than to what we were saying. It wasn't pleasant, but it never made me doubt what we had written or doubt myself." Standing tall in the face of attack is one thing; to raise your head above the parapet for a second round is quite another. But that is what the Mearsheimer/Walt double act are doing: they have gone on the offensive with the publication of a book-length version of their original treatise.

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As night follows day, the dispute has started anew. The New York Sun has dedicated a section of its website to the controversy; Dershowitz has revved up again, calling the book "a bigoted attack on the American Jewish community"; and Abraham Foxman, director of the Anti-Defamation League, has gone to the trouble of writing his own book in riposte - and it's in the bookshops a week before The Israel Lobby appears.

There is one obvious question to put to Walt: why do it to yourself? Wasn't one stoning enough? "We did ask ourselves, did we want to go through this again?" he admits, but only to add: "It didn't take us all that long to figure out we had more to say and it was our job to say it."

By writing a 496-page book, as opposed to the original article's mere 13,000 words, the authors hope to present a more nuanced version of their case. They have taken in new examples to support their thesis, notably the second Lebanon war, which broke out in the interim, and have sought to address some of the points raised by critics.

The book follows the structure of the original article fairly faithfully, and its argument can be summarised thus: in recent years the US government has given Israel unconditional support, showering it with $3bn a year irrespective of the human rights violations it inflicts on the Palestinians. It was not always this way - think of the Suez crisis of 1956 when America stepped in to frustrate Israel's (and Britain's) ambitions. But from the 1960s onwards the relationship deepened to the extent that today American and Israeli interests are deemed by many Americans to be essentially identical.

The authors ask why this is the case, and argue that strategically there is no reason for it. The end of the cold war removed a central justification for the special relationship, as Israel no longer provided the US with a barrier to communism in the region. Post 9/11, the US and Israel are presented as partners against terrorism, but America's vulnerability to attack partly stems from its support for Israel, which has provoked hostility in the Muslim world. Nor is there a moral argument for indiscriminately backing Israel - as a towering military presence in the Middle East, Israel is no longer under existential threat.

So what explains this ongoing largesse? The authors conclude that the answer lies with the Israel lobby, a loose coalition of individuals and organisations that wants US leaders to treat Israel as though it were the 51st state. The lobby stifles debate, inhibits criticism of the Israeli occupation of Palestinian lands and maintains the special relationship despite the fact that it has become a liability both for the US and for Israel itself.

To read the full article please visit The Guardian.