An emphatic advocate of Palestinian rights has won the Democratic primary for New York City mayor by 12 points—a shocking margin that he owes, in part, to the support of an outspoken Zionist.The partnership between Zohran Mamdani and New York City Comptroller Brad Lander doesn’t just showcase an unusual alliance. It provides a road map for Democrats, whose future success will require a different kind of politics than the left currently favors: one that sets aside purity tests and commits to building coalitions across ideological divides.For many promoters of the Palestinian cause, Lander is far from an obvious ally. The city’s highest-ranking Jewish official backs Palestinian statehood and has long condemned Israeli Prime Minister Benjamin Netanyahu’s far-right government. But Lander defends Israel’s right to exist as a Jewish state—identifying himself as a “progressive Zionist”—and opposes the BDS (boycott, divestment, sanctions) movement. These views make him anathema to large swaths of the left, particularly in New York City, where even bookstores and community gardens occasionally try to ban Israel’s supporters. (One of us—Alexis—is a co-founder of Pythia Public Affairs, a political-strategy firm that advised Lander’s 2021 campaign for comptroller.)Mamdani’s campaign shows the political futility of this closed-minded approach. He and Lander organized a coalition that both liberal Jews and pro-Palestinian Muslims could embrace. Crucially, the two candidates didn’t hide their differences. Mamdani has affirmed Israel’s right to exist, but not as a Jewish state. He has also defended the slogan “Globalize the intifada,” which understandably outraged many Jewish New Yorkers and even vociferous critics of Israel. The phrase “absolutely makes me uncomfortable,” Lander told CNN. “People might mean something different, but all I can hear when you say that is Open season on Jews.” Lander acknowledged that he didn’t completely agree with Mamdani on Israel and Palestine. But, he said, “we’re not running for foreign policy. We’re running for the city of New York.”[Jonathan Chait: Why won’t Zohran Mamdani denounce a dangerous slogan?]By admitting their differences, Mamdani and Lander ultimately made their alliance more credible: They encouraged voters to prioritize shared goals, not ignore disagreement. Each persuaded his supporters to place the other one second on their ranked-choice ballots, which gave a significant boost to Mamdani. The effect was particularly evident in the district that Lander once represented on the city council—an area that’s home to the largest Reform Jewish congregation in Brooklyn as well as several Conservative synagogues, yet still resoundingly backed the Muslim Mamdani. Across the city, Lander’s supporters almost certainly made up the bulk of the 99,000 votes that went to Mamdani in the decisive third round of tabulation. Although the specific tactic of cross-endorsing is uniquely suited to ranked-choice elections, Mamdani and Lander’s model of coalition building can be replicated across Democratic politics.To be sure, Lander’s endorsement didn’t erase the skepticism that many in the Jewish community feel toward Mamdani. Former New York Governor Andrew Cuomo, Mamdani’s main opponent, did his best to amplify that skepticism—often cynically, as many of his Jewish critics argued. But Mamdani himself occasionally amplified it too. In late June, he shared a social-media post mourning the death of a Jewish woman. According to authorities, she had been attacked by a man who shouted that he wanted to “kill all Zionist people.” But Mamdani neglected to acknowledge the role that anti-Semitism played in her death, much less the role that many of his ideological peers have played in fomenting anti-Semitism. The oversight invited another round of blowback.Still, Mamdani made a greater effort to appeal to Jewish voters than many of his fellow progressives have. During the campaign, he condemned Hamas’s October 7 attacks as a war crime. And when he criticized Israel, he made a point of quoting Israelis, including former Prime Minister Ehud Olmert and the historian Amos Goldberg. Immediately after Mamdani won the primary, his campaign made clear that he would continue making an effort to reach out to the Jewish community. On election night, he pledged to “reach further to understand the perspectives of those with whom I disagree.”This approach separates Mamdani from the Democratic Socialists of America, of which he’s a member. The group’s national leadership includes defenders of Hamas, and many of its chapters have demonized Zionism. Last year, DSA withdrew its endorsement of Alexandria Ocasio-Cortez, one of democratic socialism’s most popular exponents, in part because she attended an event focused on combatting anti-Semitism. This kind of exclusionary politics has led many Jews to conclude that they are unwelcome or unsafe on the left, even though some Zionists agree with much of the left’s platform. Many Zionists (including Lander) support a cease-fire in Gaza, for example, and oppose the occupation of Palestinian territories as well as settler violence in the West Bank. The left has often alienated these voters by enforcing an anti-Zionist orthodoxy.[Michael Powell: The magic realism of Zohran Mamdani]As Mamdani prepares for the general election, he would do well to avoid getting dragged into fights about Israel. This doesn’t mean he needs to reverse his positions. It means he should continue focusing on issues—such as housing, transportation, and food security—that made up the core of his campaign and animate a broad share of New Yorkers.If Mamdani wins office, he can look to London Mayor Sadiq Khan for a model of coalitional progressive politics. A Muslim member of the Labour Party, Khan was reelected to a third term last year thanks to significant support from Muslim and Jewish voters. He earned the trust of these groups by addressing both Islamophobia and anti-Semitism, and by adopting priorities—such as free school meals and affordable housing—that were popular well beyond his electoral base.If the left wants to prove that it can run the largest municipal government in America, it can’t double down on ideological purity, whether about the Middle East or anything else. Anti-Israel hard-liners will have no choice but to work with people they previously deemed pariahs. Mamdani and Lander just showed them how rewarding that collaboration would be.