President Biden was speaking at a campaign event in Minneapolis recently when a rabbi stood up and yelled that Biden needed to back a cease-fire in the Middle East.

Biden replied that he supports a pause in the fighting between Israel and Gaza until more Hamas-held hostages can be released. Security officers then escorted out the heckler as she sang “cease-fire now,” while others in the audience chanted, “Four more years.”

Biden told the crowd that he understood the conflict was emotional for many. “This is incredibly complicated for the Israelis,” he said. “It’s incredibly complicated for the Muslim world, as well.”

The rare heckling of the president at a Democratic fundraiser encapsulated an impassioned divide that is dividing the party more than any issue in recent memory. These raw emotions, focused on Israel’s conduct in the aftermath of the Oct. 7 Hamas attacks, threaten to inflame disputes among Democrats for years to come, at a time when the party had otherwise maintained a notable unity in the face of Republican disarray.

And the collision is increasingly erupting in public, creating a spectacle of division.

When Biden recently addressed an LGBTQ+ group, an audience member interrupted by shouting, “Let Gaza live! Cease-fire now!” When Vice President Harris spoke at Northern Arizona University on Oct. 17, a student pressed her about “crimes committed against those in Palestine.” At the first campaign event for Rep. Dean Phillips (D-Minn.), who’s running a long-shot race for president, Phillips found himself in a heated back-and-forth over Israel with an attendee, who was removed.

At town halls and pro-Israel rallies, crowd members boo and shout. A Jewish Democratic group is running ads against Rep. Rashida Tlaib (D-Mich.), a Palestinian American and outspoken advocate for Palestinians.

After nine House Democrats voted against a resolution condemning Hamas, Rep. Josh Gottheimer (D-N.J.) wrote on X, formerly know as Twitter, that they “are despicable and do not speak for our party.” Rep. André Carson (D-Ind.), among those opposing the measure, retorted to CNN the next day that Gottheimer was a “coward” and a “punk.” Gottheimer later vowed to disagree with his colleagues more charitably.

While most elected Democrats remain strongly supportive of Israel, more of the party’s voters now say their sympathies lie with the Palestinians than with the Israelis, according to a Gallup poll published in March.

Israel’s current attacks in Gaza appear to be bolstering that sentiment. On Friday, Israeli Prime Minister Benjamin Netanyahu rejected pleas from the United States for a bombing pause, while an Israeli strike on an ambulance killed 15 people, according to the Gaza Health Ministry.

Other issues have previously exposed divisions between liberal and moderate Democrats. Progressives argued after the 2010 signing of the Affordable Care Act that it did not go far enough, for example, and tens thousands of people protested economic inequality during the Occupy Wall Street movement in 2011.

The party’s factions had reached something of an informal truce in recent years, as Biden pushed through progressive legislation and Democrats unified against former president Donald Trump, but the schism over Israel’s attacks on Gaza — and how the United States should respond — have brought the dispute to a new level of ferocity. The long-running conflict between Israel and Palestinians is deeply personal for many Americans, especially those with Jewish or Arab roots, and outbreaks of antisemitism and Islamophobia in the United States have brought emotions to a boil.

The split has become increasingly apparent in recent weeks as officials and voters spar over the United States’ approach to the conflict, which the Biden administration fears could spiral into a broader war. More than 1,400 people were killed in Hamas’s Oct. 7 rampage through Israel, while the Gaza Health Ministry says more than 9,000 people have since been killed in Gaza.

Demonstrators have been arrested at the White House. Government officials and staff members have resigned. Rep. Ilhan Omar (D-Minn.) in mid-October reposted a cartoon posted by Yanis Varoufakis, a former Greek finance minister, on X that shows Biden telling Netanyahu, “We support Israel’s right to defend itself with any war crime of its choice.”

After Gottheimer criticized Omar and other Democrats who voted against the resolution to condemn Hamas, he softened his tone.

“Right now, many people are hurting, and it’s more important than ever for us to talk to each other,” he wrote on X. “Moving forward, that is my commitment to all of my colleagues on both sides of the aisle.”

The dissent has been particularly pronounced among younger progressives and Arab and Muslim communities, and that is likely to escalate as Congress continues to debate Biden’s request to send Israel about $14 billion in aid. The Republican-controlled House passed a bill Thursday tying Israel funding to cuts to the Internal Revenue Service, a measure that the Senate says it will not take up and that Biden has promised to veto.

Former Rep. Steve Israel (D-N.Y.) said while the divide among Democrats is real, it is not insurmountable. He urged the Biden administration not to make national security decisions based on electoral considerations as a presidential election year approaches.

“You can’t give Hamas a break in Gaza because you’re concerned about voter turnout in Brooklyn,” Israel said in an interview.

Some elected Democrats have made efforts to remind each other that they share common values. The White House has emphasized that Biden is pushing for humanitarian aid to Gaza and has called for pauses in the fighting, even as he believes Israel has a right to defend itself. The president has also repeatedly drawn a distinction between Hamas militants and Palestinian civilians.

Rep. Jamie Raskin (D-Md.) pushed Israel to seek to protect Gazan civilians while waging a “just war” of self-defense. Rep. Alexandria Ocasio-Cortez (D-N.Y.), who has called for a cease-fire, said the family members of hostages have told her they support both innocent Israelis and Palestinians who are in harm’s way.

“I believe deeply that the majority of people of all kinds do not want to see Gaza leveled and innocents killed, & that they feel and hold the pain of Israeli families destroyed,” Ocasio-Cortez wrote on X.

Sen. Chris Murphy (D-Conn.), a staunch supporter of Israel and a member of the Senate Foreign Relations Committee, issued a statement on Thursday supporting Israel’s right to defend itself — but also saying it must change course.

“The current rate of civilian death inside Gaza is unacceptable and unsustainable,” Murphy said. “I urge Israel to immediately reconsider its approach and shift to a more deliberate and proportionate counterterrorism campaign, surgically targeting Hamas and Islamic Jihad leaders and terrorist infrastructure while more highly prioritizing the safety of civilians in accordance with the law of armed conflict.”

As the war unfolds, the divide may be harder to bridge.

Some Democrats calling for a cease-fire are newly at risk of facing primary challenges. Omar and Rep. Cori Bush (D-Mo.), among others, have drawn Democratic challengers who cite their criticism of Israel as a motivating factor.

Tlaib has been a particular source of angst for some fellow Democrats. The House briefly entertained a motion to censure her over her comments on the war before voting to table the measure. And the group Democratic Majority for Israel released a TV ad on Thursday attacking her for her positions on the conflict.

Central to some Democrats’ anger were Tlaib’s remarks blaming Israel after an explosion at a hospital in Gaza last month. While Hamas initially blamed Israel, Israel denied responsibility, and U.S. intelligence officials have since said they believe the culprit was an errant Palestinian rocket. Tlaib, however, refused to retract her statement.

“You are on the right side of history,” she told protesters at a pro-Palestinian rally outside the U.S. Capitol last month.

At a pro-Israel rally in Boston last month, Sen. Edward J. Markey (D-Mass.) was booed when he called for “a de-escalation of the current violence.” Moments later, Rep. Jake Auchincloss (D-Mass.) seemed to directly contradict his colleague.

“De-escalation is not possible when they are taking hostages,” Auchincloss said to cheers. “And Israel did not ask America to de-escalate on Sept. 12, 2001.”

The confrontation at Phillips’s campaign event began with a 23-year-old Democrat standing up to ask Phillips to call for a cease-fire. Phillips responded by asking her how she feels about “Israeli babies” and “hostages in Gaza who were brutally murdered.” He said he was horrified by seeing “Palestinians slaughtered,” but did not answer the voter’s questions about a cease-fire.

The event in New Hampshire eventually devolved into a shouting match, and an audience member accused Phillips of gaslighting the voter before walking out. More people chimed into accuse Phillips of gaslighting.

Staffers then escorted the voter out of the town hall.