Haggai has a very interesting post on The Israel Lobby, the problems with Walt and Mearsheimer's methodologies, and some alternative hypotheses worth considering. I think Haggai overweights the Spiegel book, which seems to focus on presidents who served before the Israel Lobby, in its mature form, came into being (JJ Goldberg, in his book Jewish Power, dates the emergence of the modern Israel lobby to the Carter/Reagan era, and I think he's right on that). That said, the rest of the post is interesting, particularly the bit focusing on Bush's ideology as to the Israeli-Palestinian conflict. It's particularly interesting to note his initial disengagement with the issue, which later was replaced by a one-sided engagement with the issue.
But here comes the problem: Take president, like Bush, who's basically uninterested in the conflict, but insofar as he is interested, tilts towards the Israeli side. What tends to happen then is that he outsources Israel policy to the strongest, best-organized voices that he finds sympathetic. In this case, that was the Israel Lobby, which rather masterfully took charge of the situation. Again, this is what lobbies are supposed to do. But just as Labor is supposed to balance Business and Trial Lawyers are supposed to balance Deregulators, there's no one balancing the Israel Lobby -- neither other lobbies, nor any substantial number of politically-opposed politicians.
In the end, I largely agree with Haggai's criticisms. Walt and Mearsheimer's book is, at times, quite shoddy, and shouldn't be taken by anybody as gospel truth. But they've actually opened up the discussion on how American policy towards Israel actually gets made, and whether you believe their version, or Haggai's version, or Daniel Levy's version, the answer is clearly "dysfunctionally." And that's well worth exploring, and too important to be drowned out beneath cries of anti-semitism.