Ten days ago, the Jerusalem Post held a conference in New York, and inadvertently exposed the most important trend in American Jewish politics: the collapse of the “pro-Israel” center.It happened when Alan Dershowitz began telling the crowd about his plan to revive negotiations in pursuit of a two state solution. Dershowitz is legendary for his ferocious attacks on Israel critics like Jimmy Carter and Richard Goldstone. But at the Jerusalem Post conference, he found himself under attack as the audience booed and jeered his claim that Palestinian leader Mahmoud Abbas might negotiate in good faith. The crowd was far more impressed with Dershowitz’s co-panelist, Jerusalem Post columnist Caroline Glick, who demanded permanent Israeli control over the West Bank and condensed her solution to Iran’s nuclear program into two words: “bombs away.” She got a standing ovation.

To understand the incident’s significance, it’s important to understand that Dershowitz—along with people like Abe Foxman and Dennis Ross and institutions like AIPAC—defines the American Jewish mainstream. For more than a decade, that mainstream has been liberal on domestic issues, secular in its approach to Israel, rhetorically supportive of the two-state solution and adamant that the failure to achieve that solution rests with the Palestinians. And for more than a decade, support for this American Jewish mainstream has depended on a particular species of American Jew: the “secular tribalist.”

For secular tribalists, Zionism is less an outgrowth of religious commitment than an alternative Jewish identity in place of religious commitment. Their tribalism makes them instinctive defenders of Israeli action. But their secularism puts them at odds with the GOP on key domestic issues, and inclines them to root their support for Israel in the language of democracy and security, not theology. This in turn inclines them to support the two-state solution—at least rhetorically—because they don’t see controlling the West Bank as a religious imperative.

But these secular tribalists are a dying breed. Their children—who have grown up in an America where social distance between Jews and gentiles has all but collapsed—are just as secular as their parents, but less tribal. They’re less committed to Israel because they’re less committed to the idea of Jews as a distinct and embattled people. And those who do care about Israel are more likely to see it as powerful than as victimized, in part because that’s how they see themselves. Their universalism inclines them to a greater concern for Palestinian human rights, and thus, a more public opposition to Israeli policy.

As these secular Jews exit the institutions of mainstream American Zionism—either because of indifference or alienation—those institutions are being remade by Orthodox Jews for whom Zionism is not a substitute for religious commitment but an outgrowth of it. These religious Zionists are not wedded to the Democratic Party because they’re not wedded to cultural liberalism. (Orthodox Jews have voted Republican in every presidential election since 2004.) Because they’re not cultural liberals, they’re more comfortable building alliances with the Christian right. And they’re strongly influenced by their counterparts in Israel—the “national religious”—who under leaders like Naftali Bennett loudly espouse permanent Israeli control over most of the West Bank.

In a sense, what has happened among American Jews mimics what has happened among Americans more generally: A cultural gulf has opened between the religious right and the secular left, and its becoming harder and harder for the center to hold. Five years ago there was no J Street, which unlike AIPAC and Dershowitz, urges the American government to pressure the Israeli government to change course. But there was also no Emergency Committee for Israel, which unlike AIPAC and Dershowitz, disdains the Democratic Party and liberalism in general. As both the Jewish left and the Jewish right grow, the center is being squeezed.

Consider what has happened in just the last couple of years. New York Times columnist Thomas Friedman was once a pillar of the American Jewish mainstream. For roughly two decades following the 1989 publication of From Beirut to Jerusalem, he was among the most sought after speakers on the American synagogue circuit. But in recent years, as his criticisms of Israeli policy have grown sharper, he’s become a key target of the emboldened American Jewish right. Indeed, it’s no longer uncommon to find American Jewish hawks calling “anti-Israel,” if not borderline anti-Semitic.

Or consider what’s happened to AIPAC. Last summer, the group blessed a Democratic platform that didn’t include language about Jerusalem being Israel’s capital, and then panicked as right-wing groups like the Emergency Committee and the Republican Jewish Coalition savaged the platform—and implicitly AIPAC itself—as anti-Israel. A few months later, when President Obama nominated Chuck Hagel to be defense secretary, AIPAC—which couldn’t afford to alienate a sitting administration—took no public position. And as a result, the group was forced to watch from the sidelines as J Street and the Emergency Committee publicly battled it out, raising the profile of both groups.

Don’t get me wrong: The American Jewish center remains larger and more powerful than either the Jewish left or the Jewish right. But the gap is shrinking. It’s shrinking because of the growing divide between secular and religious Jews in the United States. And it’s growing because as Israel entrenches its control of the West Bank—and as a younger generation of Israeli hawks call for making that control permanent—it becomes harder to square support for the two-state solution with support for Israeli policy. Increasingly, American Jews are choosing one or the other, thus making the very choice that the American Jewish mainstream has long sought to avoid.

After his experience at the Jerusalem Post conference, Dershowitz now says “I will no longer lend my support to ‘far right pep’ rallies of the kind I spoke at last week.” Fair enough. But on both left and right, the pep rallies are only growing louder. And what’s growing quieter is everything in between.