What does it mean to be “pro-Israel”? Last Thursday night, two of Philadelphia’s bedrock Jewish institutions—the Jewish Federation of Greater Philadelphia and the Hillel Foundation for Jewish Campus Life—sponsored a film screening and panel discussion at the University of Pennsylvania on the topic. Headlined by Alan Dershowitz, the retired Harvard Law School professor who for decades has been an outspoken American advocate for Israel, the event aroused a hostile reaction in the community even before it took place. Sharply worded op-eds appeared in local newspapers and protestors leafleted the venue. But the hubbub was generated not by Palestinian solidarity groups, but by liberal Zionists– partisans of J Street, the dovish “pro-Israel” lobbying outfit founded in 2008 to counter AIPAC’s hardline message.

The film in question, “The J Street Challenge,” is a slickly produced far-right assault on the “pro-Israel, pro-peace” organization. Produced by Americans for Peace and Tolerance, one of a growing number of right-wing Zionist groups with Orwellian names, the film mostly showcases the perspectives of hardcore Jewish ethno-nationalists. J Street’s complaint was the sponsorship: why was such a scurrilous attack on one of its own being aided and abetted by the mainstream Jewish establishment?

But as it happened, the debate over J Street turned out to be peripheral to a much more interesting contretemps. What transpired—the intermittent pandemonium and racist hysteria of the Q&A session, the evident tensions between Dershowitz and his co-panelist, and the fact that it all went down under the auspices of mainstream Jewish community groups—is the best evidence yet that an increasingly panicked and isolated right-wing donor base is waging a scorched earth campaign against the very foundations of contemporary American Zionism. To understand why this is the case, it’s important to first know something about the challenge that J Street represents.

Since it was created, J Street has capitalized on the wave of disaffection—from Israel, and from the Jewish establishment’s slavish deference to right-wing Israeli governments—that began overtaking college-aged American Jews during the last decade. That wave resulted from a confluence of factors: the collapse of the Oslo peace process, the rise of a right-wing consensus in Israel, the shocking brutality of Operation Cast Lead, the assimilation into college textbooks of revised narratives about the expulsion of Palestinians in 1948, and the growing challenge of the Boycott, Divestment, and Sanctions (BDS) movement. J Street’s raison d’etre is channeling American Jewish support for the two-state solution and pushing a limited conception of Palestinian rights, even at the risk of taking on sitting Israeli governments.

J Street’s primary target is Jews who have fully assimilated into the American liberal tradition but who continue to feel an emotional connection to Israel. Despite the group’s occasional concessions to the right on issues like unlimited military aid to Israel, and its opposition to the BDS movement, the proclivities of its member base are known by insiders to be more liberal than Zionist. Many J Streeters identify themselves as anti-racist and universalist. In other words, they are liberals with a thin candy coating of Zionism.

For decades prior to the establishment of J Street, the Zionist right lived in a marriage of convenience with liberalism, embodied by no one better than Alan Dershowitz. The bargain was this: the far-right ethno-nationalists would cede public leadership of the pro-Israel movement to “liberals” like Dershowitz on the condition that those liberals did nothing of any real consequence to challenge the far right’s expansionist designs on a Greater Israel. Until the emergence of J Street as a credible counterforce (courted by the Obama administration and making slow headway in Congress), the liberals were safely contained. Movement figures like Dershowitz—a famous civil liberties lawyer, never mind his endorsement of “torture warrants” and collective punishment—could be trusted to brandish their own commitment to liberal values, impart Israel with a veneer of progressivism by association, all while never breaking publicly with the official line of right-wing Israeli governments.

Now a group of Jewish liberals has gone rogue. The right is furious, and the intermediary role of people like Dershowitz is becoming increasingly untenable.

All this is the political backdrop to the screening of “The J Street Challenge.” The film stars a phalanx of credentialed Zionist ultras, including Dershowitz himself. But a closer look reveals Dershowitz as an outlier among the film’s dominant lineup of openly illiberal ethno-nationalists. This includes people like Jerusalem Post editor Caroline Glick, whose latest book is perhaps the first mainstream English-language tract in decades to openly call for a unitary Jewish state in all of historic Palestine. Daniel Gordis, author of a recent Menachem Begin hagiography, laments that American Jews no longer believe in nation-states or find value in unadulterated ethnic solidarity. One representative from the media watchdog CAMERA dismisses the very notion of universality. For her part, Glick’s naked condescension and scorn for liberals is exceeded only by Harvard professor Ruth Wisse. Eyes wild with conviction, Wisse brings the film to a climax—and raised a cheer from the audience—when she denounces the rank “stupidity” of anyone who doesn’t see the Israel-Palestine conflict as but the latest worldly instantiation of a trans-historical war against the Jews.

The key point is that these figures are mounting an assault not on J Street or liberal Zionism but onliberalism itself. They drip with sarcasm at the very suggestion that all men are created equal. It’s alone among them that Dershowitz uses his screen time to enumerate Israel’s liberal democratic achievements. For the others, these things are simply beside the point: the time for make-believe is over. You’re either with us or against us.

Alongside Dershowitz on the Q&A panel was Charles Jacobs, the film’s producer. A one-time deputy director of CAMERA and the founder of Americans for Peace and Tolerance, Jacobs recently spearheaded a successful campaign to pressure the administration of Northeastern University in Boston to disband its campus chapter of Students for Justice in Palestine (SJP). The first to question him was a representative of University of Pennsylvania’s AIPAC student group. The line of inquiry was surprising: Couldn’t pro-Israel groups, he asked, reach a wider audience if they were able to co-host events with Students for Justice in Palestine (as is currently prohibited by national Hillel guidelines)? Jacobs sharply rebuffed him: SJP is an arm of Hamas, and appeals to pluralism and “free speech” are a Trojan horse used by the far left to infiltrate anti-Semitism into Jewish spaces. The student tried to object, but the MC asked that he take his seat. The audience, too, had had enough of him.

From that point forward, things took a surreal turn. Speaker after speaker stepped to the mic to lambaste Dershowitz, often in the most abusive terms, for a wide variety of crimes: for referring to the “West Bank” instead of “Judea and Samaria”; for Dershowitz’s anti-Semitic denial of the right of Jews to colonize the Palestinian city of Hebron; for encouraging his followers to vote for the Jew-hater Barack Obama; and, of course, for his failure to comprehend the savage, homicidal nature of Islam. Dershowitz attempted to defend himself, comparing his assailants to Meir Kahane and denouncing their racism. But his appeals were barely audible over the shouted cross talk and frenzied cheers of the audience. “If you don’t want people like me defending Israel,” he told them, “then you’re in serious trouble.”

To anyone not hermetically ensconced in the far-right moral universe engineered by wealthy activists like Jacobs and billionaire Republican financier Sheldon Adelson (and few of the hundreds in attendance were not), the whole scene was insane. It was a topsy-turvy world where Alan Dershowitz and young AIPAC devotees represent the despised far left wing of the “official” Jewish conversation about Israel. But this was not the meeting of some fringe group in a synagogue basement. It was a big, Federation-sponsored production at a prestigious university.

Young American Jews are getting off the pro-Israel bus, and the fury of the right-wing donor base—its uncalculated reaction to the sudden loss of control—is poised to further erode the historic bargain between Zionism and liberalism that kept the wheels in motion for so many years. As J Street members move further to the left and the Jewish world turns bimodal—pure universalism vs. pure ethno-nationalism—we’re likely to see more of these insurgent encroachments by the far right into mainstream spaces. With the Dershowitzian compromise on life support, the internal dynamics of Jewish institutional life are about to get very, very interesting.

Matthew Berkman is a Ph.D. candidate in political science at the University of Pennsylvania. He is writing a dissertation on American Jewish politics.