Matt Yglesias, writing at The American Prospect, triggers some more thoughts in the same vein for me:
The parties to the conflict aren't really in need of any brilliant new substantive ideas from the United States -- the basic shape of what an agreement would look like is well understood. Nor are our services as mediators really needed -- the Norwegians have proven capable of playing that role when asked, and no doubt others could do the same. What's needed is something that changes the Israeli domestic calculation -- a sense that the nature of the Israel-U.S. relationship will depend, in part, on the nature of Israeli policy vis-a-vis the Palestinians. Any administration willing to publicly chastise an Israeli government will inevitably wind up ruffling some feathers and taking political heat for it, but it will almost certainly be for the Israelis' own good. Jimmy Carter's tough-love approach didn't win him any fans among Israel's most strident supporters, but at the end of the day, the resulting Egypt-Israel peace treaty has been enormously beneficial to Israel.
To me, the first bit--about the U.S.'s superfluity--recalls my discussion of the perceived need to revive the U.S.'s dominance as a global hegemon and settler of disputes through some kind of perceptible improvement in the Israeli-Palestinian situation.
The point Yglesias makes that the only real motivator will be a change in "the Israeli domestic calculation" is a good one, and this is the first time I've seen it made. It's also the best argument for U.S. non-superfluity: that Israel might regard American disfavor as dangerous enough to change its behavior. It would depend, of course, on exactly what "disfavor" would mean, but Yglesias's formulation ("the nature of the Israel-U.S. relationship would depend...on the nature of Israeli policy") suggests a pretty fundamental potential shift: from cherished allies to, well, not (that is the "nature" of the relationship, no?).
In that case, then yes, I think that could be a strong incentive to Israel to change. I'm just not sure this is realistic. I don't know whether Israel ever really felt threatened in its status as a U.S. ally under Carter, but it's very difficult to imagine any American president actually punishing Israel severely enough to suggest that "the nature of the relationship" had changed. I agree with Yglesias that it could be effective, but I don't know that it's likely. He nods to that difficulty in further paragraphs, but even in a scenario where, say, military aid got reduced, I'm not sure I would say that the relationship had changed so much as that a message had been sent.
But, of course, I could be wrong.