Megan speaks up in its defense - arguing, inter alia, that the rump, terrorist-run Jewish Gaza in Stephen Walt's hypothetical would still have a potent lobby in the United States for the same reason that there's long been sympathy among Irish-Americans for the interests of the stateless, terror-producing members of the IRA. She also suggests that the influence of the Israel lobby in the United States is best explained by ethnic affinities - not only the ethnic loyalties of Jewish-Americans, but the quasi-ethnic affinities of "evangelical Christians who think of themselves as in some way descended from the ten tribes of Israel."  

To the first point, I actually think the Irish example tends to weaken Walt's counterfactual.   The major point of the thought experiment was Walt's insinuation that a Jewish Hamas wouldn't be denounced as terrorists in Washington the way the Arab Hamas gets denounced - because of the influence of the Israel Lobby, presumably. And the example of Northern Ireland suggests precisely the opposite. Yes, even a stateless, terrorism-prone Jewish group in the Holy Land would doubtless have sympathizers in the United States, just as the Irish Republican Army did in the 1970s and '80s. But despite the sympathies of some Irish Americans for the rebels in Northern Ireland, and the dalliances of the occasional American politician with Gerry Adams and Co., the IRA was on the State Department's list of, yes, terrorist organizations until the Good Friday Accords. And it's pretty easy to imagine how the American government would have responded if Catholic nationalists had taken power in a swathe of Northern Ireland and started launching missiles across the Irish Sea into Scottish and English townships. (It's also worth noting, as long as we're drawing analogies, that the IRA's charter was just slightly less objectionable than Hamas's ...)

To the broader point about the roots of America's affinity for Israel, I suppose I agree to some extent with Megan's suggestion that "we are the Israel lobby, to a greater or a lesser extent - all Americans who think of themselves as more like the Israelis than the Palestinians." (This is, of course, one of the reasons why it doesn't make sense to analyze American support for Israel primarily or exclusively in terms of the machinations of a lobby - unless you're interested in giving the whole thing a conspiratorial gloss, that is.) But as to why many Americans - be they Evangelicals or whomever - think of themselves as more like Israelis than Palestinians, I'm largely in agreement with a friend, who writes of Megan's post:

Evangelical Christians' identification with Israel is not an "ethnic affinity." For starters, evangelical Christians do not actually believe they are descended from the ten tribes of Israel. (I suppose Mormons believe that, but they are a negligible fraction of Israel's supporters in America.) Is it not obvious that the affinity of evangelical Christians for Israel is religious and cultural?
 
And this business about how "almost all Americans see Israelis as sharing a common European cultural heritage that the Palestinians do not" because of something "rooted deeply in our genes" like "our selfish alleles"?  Maybe the identification with Israel as being part of a common cultural heritage is rooted deeply in -- oh, I don't know -- our common cultural heritage: Like that Israel actually is part of Western civilization, is a child of European cultural and political traditions, and belongs to the family of liberal democracies while Hamas is a theocratic terrorist organization bent on destroying Western civilization, or at least its influence in their neighborhood.
 
The answer to Stephen Walt's query is obviously "Yes" -- but not only because in his hypothetical scenario the Israel Lobby would not exist. It's also because American support of Israel, and even the Israel Lobby's support of Israel, is not unconditional, but based on these religious, cultural, and political affinities and principles. AIPAC and similar folks opposed those Jews who refused to evacuate Gaza to make way for a Palestinian state -- and those Jews were not nearly the lunatics and terrorists that Walt describes in his hypothetical.
 
Now, precisely because of cultural reasons, I don't think Walt's scenario would ever come to pass -- for cultural reasons, too, the Jewish refugees from Arab lands behave nothing like the Arab refugees from Israel -- but if it did, of course the United States would denounce the Jewish Hamas that Walt imagines. I would too.

Finally, to Megan's follow-up post on the merits of The Israel Lobby, I would just reiterate a point I made in my recent Bloggingheads session with Matt Yglesias: I don't think that critics of AIPAC's influence on American foreign policy, and the America-Israel relationship more generally, are serving their cause by expending a lot of energy sticking up for a lousy book about the subject - especially, as in Megan's case, when they themselves admit that it's a lousy book - just because its authors were subjected to unfair attacks along the way to fame and sales figures beyond the dreams of the average IR theorist.