When Barack Obama asked veteran foreign policy expert Zbigniew Brzezinski to introduce him in Iowa this week, the Democratic presidential candidate found himself under attack from pro-Israel activists such as Harvard professor Alan Dershowitz.
Dershowitz warned that Obama had made "a terrible mistake" in keeping company with Brzezinski, a former national security adviser in Jimmy Carter's administration.
The problem was that Brzezinski had written a favourable review of The Israel Lobby and US Foreign Policy, the controversial 2002 paper by Chicago political scientist John Mearsheimer and Harvard international relations professor Stephen Walt, which has now been expanded into a book.
"I think this shows how relentless some of these groups and individuals will be to try and make sure that the views that we expressed are never taken seriously," Walt tells me when we meet in his office at Harvard's John F Kennedy School of Government this week.
"And I think the reason for that is that, first of all, we're right and, second of all, the counter-arguments are actually quite weak. And if the counter-arguments are quite weak then you've got to make sure that the correct arguments don't get heard and don't get taken very seriously. And I think this little flap over Prof Brzezinski and over Barack Obama is in fact just more evidence that we're correct."
Walt and Mearsheimer argue that what they call the Israel lobby, a loose collection of pro-Israel groups, has successfully distorted US foreign policy in a way that operates against the American national interest and often against Israel's long-term interest. They maintain that key figures in the lobby were instrumental in making the case for war in Iraq and are now leading the call for a US military attack on Iran.
Both foreign policy "realists", the authors believe that there is no strategic or moral justification for what they describe as the unconditional support Washington gives Israel.
"In terms of enhancing America's security, Israel is probably a net liability at this point. I think you can make the case that during the Cold War, Israel was something of a strategic asset vis-a-vis Soviet client states. I think that's not an open-and-shut case, but you can certainly make a pretty good case for that," Walt says. "But of course, once the Cold War ended, that value disappeared, and now giving Israel unconditional support generates anti-Americanism in the Middle East.
"It is one of the reasons the US now has a serious terrorism problem. It undermines our relations with other allies who think our policy is unwise and somewhat morally questionable as well . . . If you weigh the benefits and the costs, the costs are now much greater than the benefits."
THE ORIGINAL ARTICLE was first commissioned by the Atlantic Monthly but, after a number of drafts and modifications, the magazine decided not to publish it, a decision Walt believes to have been motivated by cold feet.
"We had consulted quite closely with the editor and the version that we ultimately sent them was one that conformed almost identically to what we had planned, what they had seen in earlier drafts, the modifications they'd asked for. So we gave them the article that they said they wanted," he says. "What I believe, though I have no direct evidence, is that when they got the final manuscript they thought hard about it and they decided it would be too controversial, that it would have negative consequences for their revenue base - people would cancel subscriptions, people might cancel advertising - and they just didn't want to take the heat of trying to publish it."
When it appeared in the London Review of Books, Mearsheimer and Walt faced accusations of anti-Semitism, with some Jewish groups claiming that they were rehashing a dangerous conspiracy theory similar to the 19th-century fraud, The Protocols of the Elders of Zion, which suggested that an international Jewish cabal controlled world events.
In fact, both Walt and Mearsheimer describe themselves as sympathetic to Israel and, in a European context, their views on the Israel-Palestine conflict would be close to the mainstream of public opinion.
"I'm a strong supporter of Israel's right to exist and to live in security and prosperity in the region. I think that many centuries of anti-Semitism in Europe and elsewhere provide a very strong moral argument for a Jewish state and I think the United States ought to be willing to come to Israel's aid if its survival is ever in jeopardy," Walt says.
Although Walt respects those in Britain and Ireland who are calling for an academic boycott of Israel and rejects claims that their campaign is anti-Semitic, he is sceptical about the boycott.
"I don't like anything that interferes with intellectual exchange and academic freedom. I think intellectuals and academics should really be able to interact with each other as much as possible, and having Israeli academics come to England is an opportunity to talk to them about what's going on in that part of the world," he says. "Second of all, I don't like any form of collective punishment and this is again a way of punishing an entire category of people, many of whom may not support the policies that are objectionable."
Walt describes the Israel lobby as similar to other social movements in the US, such as the environmental movement or the farm lobby - but much more effective. He points to the influence of groups like the American Israel Public Affairs Committee (Aipac) on members of Congress and on presidential candidates.
"Congressmen know that if they take positions that are contrary to, say, what Aipac wants, they're going to face trouble. They're going to have letters written in their local districts. They're going to find that they can't get campaign contributions as readily - and, in fact, if they're not careful, campaign contributions will flow in large amounts to their opponents," he says. "And there are more than half a dozen clear cases in the last 20 or 30 years where Aipac or others have targeted incumbent politicians who weren't doing what they wanted and drove them out of office.
"Do that a few times and everybody else observes it, which is why when Middle East issues come up, you don't have much of a debate on Capitol Hill. Resolutions that are pro-Israel pass overwhelmingly - you know, 400 votes in favour, 10 votes against. This is quite unusual in American politics."
SOME CRITICS OF Walt and Mearsheimer, including Noam Chomsky, complain that they misunderstand the nature of the US-Israel relationship and that Israel in fact acts as the instrument of a wrong-headed US policy in the Middle East. Walt insists that recent events contradict that analysis, pointing to US support for Israel's war against Hizbullah in Lebanon last year.
"If we were the dog and Israel were the tail, you would have seen a very different policy in Lebanon in summer of 2006. Here was a case where the Israelis were going after Hizbullah in a quite foolish fashion and in ways that we should not have ever approved," he says. "And that was undermining the government that the US wanted to support. If it was Washington telling Jerusalem what to do, we might have told them to go after Hizbullah, but we would have said, 'for God's sake don't attack the rest of Lebanon and don't bomb Beirut'."
Walt says he has received far more messages of support than hate mail for the article and the book and that the controversy was less personally traumatic than many people think.
He believes that the debate over Israel in the US is beginning to open up and starting to reflect the more nuanced view of the American public, which favours a more conditional relationship.
"Americans like to be able to talk about difficult subjects and everybody in the United States understands that our policy in the Middle East is deeply screwed up and that we face an enormous number of serious problems there," he says.
"Iran is a problem. Hamas is a problem. Hizbullah is a problem. Saudi Arabia and some of the things going on there are a concern. Iraq is a disaster. The Israel- Palestinian conflict is tragic for the Israelis and tragic for the Palestinians.
"So there's a mess there and if we in the United States, given our influence in the region, given how important a role we have there now, if we can't have a civil conversation about our different policy options and the different groups that are trying to influence those policy options, we are unlikely to come up with policies that will serve us better".