For years, AIPAC (The American Israel Public Affairs Committee) has helped to stonewall the Middle East peace process by building a solid wall around the Israeli government, protecting it from criticism in the US. Senators and representatives have feared the wrath of AIPAC come Election Day, even in states and districts where the Jewish vote is negligible. Whatever they may have thought privately about Israel's policies toward the Palestinians, they've remained silent.

    I got a first-hand glimpse of the process shortly after last year's election, when I talked to an aide of a newly elected House member. The new member, who represents a district with hardly any organized Jewish community, knew very little about the Middle East when the campaign began. The representative had been "educated" on the issue, the aide told me, by a handful of wealthy Democrats - none from the member's district, all generous contributors to the campaign, and all staunch supporters of the AIPAC line. That's how it works, all over the country.

    Or at least that's how it used to work. Now, for the first time, there are signs of a crack in AIPAC's vaunted political edifice. The wedge issue is the Obama administration's public demand that Israel stop all new construction in its West Bank settlements, including what the Israelis call expansion to accommodate "natural growth."

    Though Israel's Prime Minister Benjamin Netanyahu heads the right-wing Likud party, settlement expansion is hardly a partisan matter in Israel. It has continued at a more or less unbroken pace for years, regardless of which party headed the government. And Israeli Defense Minister Ehud Barak, leader of the opposition Labor Party, is equally staunch in demanding the right of "natural growth."

    What's new is the serious objection being voiced in the US government, not merely by the president and his administration, but by members of Congress, including John Kerry, who heads the Senate Foreign Relations Committee, and several prominent Jewish lawmakers, such as Carl Levin, chair of the Senate Armed Services Committee; Howard Berman, chair of the House Foreign Relations Committee; and influential representatives Henry Waxman and Robert Wexler.

    When they met recently with Netanyahu, they made him "very, very aware of the concerns of the administration and Congress," according to one Congressional aide. They pressed Netanyahu on the need to stop building in settlements and rejected his call for Palestinian reciprocity on terrorism as a precondition.

    (Another sign of the change: A Congressional delegation visiting Israel actually discussed, in private, the possibility of prohibiting Israel from using American weapons in the West Bank.)

    After so many years of AIPAC dominance, it would be too much to expect all Democrats to back Obama on the settlements question. There are still plenty in Congress who toe the AIPAC line.

    "We are applying pressure to the wrong party in this dispute," said Rep. Shelley Berkley. "I don't think anybody wants to dictate to an ally what they have to do in their own national security interests," said Rep. Gary Ackerman. Though he allowed that there's "room for compromise," his version of compromise sounds very much like the Israeli government's version: "I think that most people could understand somebody having a child and their child living with them, as long as it's not a ruse to expand" the settlements.

    But the fact that there is any debate at all on this issue in Congress marks a sea change in Washington, brought about by a perfect storm of converging factors.

    Most obviously, there is the administration's tough public stance on the settlement expansion. It's not easy for Democrats in Congress to buck a very popular president of their own party, especially when he's making an argument based on national interests and national security.

    Less obviously, there is a remarkable change in attitude among American Jews. Well, it's less obvious to those who get all their information from the mass media, where this change is far too little reported. But to those of us who have been working in the once-tiny American-Jewish peace movement, the growth of that movement all around us is nothing short of astounding.

    It was already evident a couple of years ago. In the last two years, the thin stream of dissent has grown steadily broader and higher. At the rate it's going, it could well become something close to a torrent sooner than anyone might imagine.

    Two-thirds of American Jews say they want the US to play an active role in moving Israel toward peace, even if it means the US publicly disagreeing with, and exerting pressure, on the Israelis. That's according to a poll conducted last summer by J Street, the pro-Israel, pro-peace lobby now widely seen as the counterweight to AIPAC. Contributions to J Street are growing at a rate faster than AIPAC's. In last year's election, of 41 candidates endorsed by J Street for their pro-peace positions, 31 were winners.

    Working closely with J Street is the grassroots Jewish-American peace group, Brit Tzedek v'Shalom, which now claims some 45,000 members and pledges of support from over 1500 rabbis and cantors. Just a few months ago, that latter number was less than 900, another indicator of how fast the Jewish community is changing.

    But numbers tell only part of the story. Inside the Jewish community, there is an intangible but unmistakable new mood of open discussion, and even debate, about Israeli policies. Politicians, whose job is to sense those intangible moods, are beginning to pick it up. More and more of them realize that the leaders of Jewish organizations who still parrot the AIPAC line may dominate the mass media, but they can no longer dominate their own rank-and-file.

    And those organizational leaders are surprisingly muted in their support for Netanyahu on the settlements issue. "Even the most conservative institutions of Jewish American life don't want to go to war over settlement policy," said David Twersky, who was until recently the senior adviser on international affairs at the American Jewish Congress.

    The convergence of a changed presidential administration and a changing Jewish community opens up room for legislators to be influenced by a third factor: common sense. These politicians are smart enough to realize that Netanyahu's demand to accommodate "natural growth" is just what Representative Ackerman fears: a ruse to expand the settlements.

    According to Israel's own Central Bureau of Statistics, some 40 percent of the growth in settlement population comes not from "natural growth" (the excess of births over deaths), but from new immigration. Since those new immigrants need not only new bedrooms, but new kitchens, living rooms, dining rooms, as well as all the expanded public services that adults require, it seems likely that well over half of the new construction is to accommodate them and not for "natural growth."

    What's more, as Israeli columnist B. Michael pointed out, when a family in Israel proper has another child or a couple gets married, their government does not provide them with new living space. They just move to new quarters, if they can afford it; if they can't, they make do with the space they already have. Why should the settlers be treated any differently?

    Indeed, since the settlers are living in their current homes illegally by most interpretations of international law, there is all the more reason that they should be expected to move back to Israel proper, where there is plenty of housing to accommodate them.

    "What the hell do they want from me?" Netanyahu reportedly complained after his talk with Obama. In the weeks and months ahead, we can expect a growing chorus in the US Congress to echo the changing views of American Jews and answer: We want you to heed the president's call to stop settlement construction completely, comply with international law, and open the door to serious negotiations with the Palestinians toward a two-state solution.

    Every time that answer is heard publicly, it widens the crack in AIPAC's wall and brings us closer to the day when that wall, inevitably, crumbles.