Knowing Too Much: Why the American Jewish Romance With Israel is Coming to an End. By Norman Finkelstein. OR Books; 472 pages; $18 and £12. Buy from Amazon.com

IT HAS become increasingly common for prominent liberal Jewish Americans to voice anguished disquiet over Israel’s behaviour. The most visible signs of this trend are books, such as Peter Beinart’s “The Crisis of Zionism”, which came out three months ago, and the growing support for the (admittedly patchy) achievements of J Street, an advocacy group that lobbies for a two-state solution to the Israeli-Palestinian impasse. In his eighth book, “Knowing Too Much”, Norman Finkelstein, an American academic who became a critic of Israel long before it was fashionable, traces the underlying dynamics of the disquiet.

Mr Finkelstein’s central claim is that American Jews’ feelings about Israel were always guided more by self-interest and personal values than by Jewish solidarity. They cared little about the country before the war of 1967, fearing accusations of “dual loyalty”. Israeli concerns, to them, were not American concerns. They rallied round after the war, Mr Finkelstein argues, chiefly because that was when Israel’s fight against the Arabs became geopolitically tied to America’s fight against the Communists.

To the extent that the ardour of liberal American Jews has cooled, this is not because, as argued by Stephen Walt and John Mearsheimer, two leading foreign-policy scholars, the end of the cold war made Israeli and American interests diverge. In fact, on most Middle Eastern issues—Islamism, democratisation, the danger of Iranian nuclear weapons—the two countries still have similar goals, although expansion of settlements in the West Bank is an obvious exception. But Mr Finkelstein argues that American Jews are becoming disenchanted because they now “know too much”. Traditionally Democratic voters, they have grown increasingly disturbed by questioning new research that is being published about Israel’s history and outspoken commentary by former President Jimmy Carter and others, who have brought home to some American Jews that their Israeli cousins were never as liberal as they seemed, and are becoming less and less so.

Mr Finkelstein makes this argument crisply and convincingly. However, it is over by page 89. The remaining four-fifths of “Knowing Too Much” might as well be a different book, perhaps more aptly entitled “You Still Don’t Know the Half Of It”: an attempt to skewer every apologist, hypocrite, dissembler and charlatan who has ever sought to paint Israel in softer shades than Mr Finkelstein thinks it deserves.

His desire to combine the two arguments is perhaps understandable. Since 1988, when he received his doctorate from Princeton with a thesis that debunked the then-popular claim that many Palestinian Arabs were not in fact longtime natives but immigrants like the Zionists, he has been a scourge of pro-Israel scholarship. His book, “The Holocaust Industry” (2000), was especially controversial because it claimed that the Jewish tragedy was being exploited in Israel’s defence. A campaign by a Harvard academic, Alan Dershowitz, who is one of Israel’s staunchest supporters, contributed to Mr Finkelstein being denied tenure at DePaul University in 2007 and ultimately resigning. He has been jobless since. It must feel like a vindication, therefore, that more American Jews are now rejecting the arguments of people like Mr Dershowitz. And it must be tempting to turn the knife by trying to take those arguments to pieces.

But the result is an unwieldy hydra of a book that, having made its point early on, lashes out in all directions to no clear purpose. Mr Dershowitz in fact comes off relatively lightly. Benny Morris, an Israeli historian who turned from critic to defender of the state, earns the epithet “raging kook”. A whole chapter is devoted to dismantling “Foxbats Over Dimona”, a book claiming that the 1967 war was essentially triggered by the Soviet Union, which, some good reviews aside, has never been taken too seriously. Mr Finkelstein also spends many pages attacking both Human Rights Watch for, as he alleges, softening its conclusions about Israel for political reasons, and Israel’s Supreme Court, an imperfect but important mitigator of the state’s worst excesses against Palestinians, for tying itself in legal and ethical knots.

Mr Finkelstein’s research is certainly thorough. His characterisations, too, can be brilliant, and he spares nobody: Yasser Arafat, the longtime Palestinian leader, suited Israel as a negotiating partner because “he possessed the nationalist credentials of a Nelson Mandela but… appeared desperate enough to play the part of the Bantustan chief, Mangosuthu Buthelezi.” This orgy of debunking distracts from the book’s main point, which is an important one. Israel has done some unpleasant things. But it still needs friends it can trust. And when they speak out, it needs to believe they may have a point worth listening to. By making his historical scholarship the handmaiden of a vitriolic vengefulness, Mr Finkelstein overplays his hand and ultimately diminishes the impact of his case.