With a giant Stars and Stripes and two gleaming cars at his back, Joe Biden turned to focus his remarks on one member of the audience. “From my heart, I pray that your grandmom and family are well,” he told Rashida Tlaib, the only Palestinian American in Congress. “I promise you, I’m going to do everything to see that they are, on the West Bank. You’re a fighter.”

It was a characteristic peace offering by the US president, even as protesters rallied outside the Ford plant in Dearborn, Michigan, and Tlaib herself challenged Biden over his unyielding support for Israel. But Tuesday’s gesture, and even a Middle East ceasefire declared on Thursday, may not be enough to heal a growing rift in the Democratic party.

Biden’s first hundred days as president were striking for their rare display of Democratic unity, pleasantly surprising the left with his ambitions for government spending, racial justice and the climate crisis. Alexandria Ocasio-Cortez, a congresswoman from New York, said his administration “definitely exceeded expectations that progressives had”.

Even when a crack appeared last month over Biden’s plan to retain former president Donald Trump’s cap on the number of refugees allowed into the US, the White House backed down within hours after fierce blowback from progressives and harmony was restored.

But Israel’s bombing campaign against Hamas in the heavily populated Gaza Strip, which killed 65 children over 11 days, was of a different magnitude. It exposed a generational and political divide in the party that cannot be so easily bridged.

On one side are Biden, 78, the Senate majority leader Chuck Schumer, 78, House speaker, Nancy Pelosi, 81, and House majority leader, Steny Hoyer, 81, all of whom grew up in a political era when reflexive support for Israel was axiomatic. Hoyer said this week: “We must not allow extremists to hijack important discussions about securing a better future for Israelis and Palestinians by promoting a false narrative.”

On the other side is “the Squad”, progressive members of Congress and people of colour who include Tlaib and Ocasio-Cortez (both called Israel an “apartheid state”), Ilhan Omar of Minnesota (who described Israeli airstrikes as “terrorism”) and Ayanna Pressley of Massachusetts (who tweeted “We can’t stand idly by when the United States government sends $3.8 billion of military aid to Israel that is used to demolish Palestinian homes, imprison Palestinian children and displace Palestinian families”).

Protesters gather and demand that Jerusalem stop expelling Palestinian people from Israel at Israel’s embassy in Washington this week.
Protesters gather and demand that Jerusalem stop expelling Palestinian people from Israel at Israel’s embassy in Washington this week. Photograph: Tasos Katopodis/UPI/Rex/Shutterstock

The generation gap reflects a broader trend among the US population. John Zogby, a pollster, notes considerably more sympathy for Palestinians among voters under 40 than those over 60. “Older folks are able to conjure up the original legend of David Ben-Gurion [Israel’s first prime minister] and the wars of 1967 and 1973,” he said. “Voters under 40 conjure up Benjamin Netanyahu [Israel’s current prime minister], the intifada and now several bombings in Gaza.”

Youth is not the only force moving the Democratic party’s centre of gravity. On Thursday the leftwing senator Bernie Sanders, 79, introduced a resolution blocking a $735m weapons sale to Israel while his colleague Elizabeth Warren, 71, welcomed the ceasefire but urged Biden to press for a two-state agreement “that starts with taking all appropriate steps to end the occupation”.

Several pro-Israel members of Congress also raised questions in recent days, a sign that, while backing for Israel’s right to self-defense remains rock solid, skepticism about its government’s treatment of the Palestinians is no longer taboo. The fact that “the Squad’s” scathing comments went unrebuked spoke volumes about how much has changed in a few short years.

Logan Bayroff, a spokesperson for J Street, a liberal Jewish American lobby group, said: “There are shifts and you see it on the left side of the spectrum with vocal and unapologetic Palestinian rights advocacy from the likes of AOC [Ocasio-Cortez] and others but you also see it reflected across a large swath of the party.

“What is notable is that we’re still not seeing that reflected in terms of policy or rhetoric from the Biden administration. I think this is less one half the party versus the other and it’s more Congress pushing in one direction and the administration not following as of yet.”

Activists and analysts suggest that various push and pull factors are at work. Netanyahu’s ostentatious alliance with Trump, whom he praised for moving the US embassy to Jerusalem from Tel Aviv, makes him a singularly unsympathetic figure for Democrats. Netanyahu fiercely opposed Barack Obama’s nuclear deal with Iran, which Trump scrapped but Biden is seeking to revive.

Donald Trump’s identification with the policies of Benjamin Netanyahu have weighed more heavily with younger Democrats than historic ties with Israel.
Donald Trump’s identification with the policies of Benjamin Netanyahu have weighed more heavily with younger Democrats than historic ties with Israel. Photograph: Ahmad Gharabli/AFP/Getty Images

Bayroff added: “When you have an Israeli leader who has identified himself so closely with the ideology, rhetoric and tactics of rightwing ethnonationalism and has explicitly echoed Donald Trump and Trumpism – as well as aligning himself with other illiberal democracies and leaders like Orbán and Bolsonaro and Modi – that’s the antithesis of the pluralistic, diverse liberal democracy that most Democratic voters and an increasing number of Americans are supporting. So that is going to lead to a collision.”

Meanwhile a new generation of Americans, including Jewish Americans, have grown up with a heightened consciousness of social justice movements. Sanders and others have compared the Palestinian struggle to Black Lives Matter and want to apply domestic principles to foreign policy.

Bayroff added: “We’re seeing an overall push in all aspects of American politics and policy from a rising generation and a lot of voters to centre human rights, dignity and equality and equal treatment and social justice for all people. When they see a 54-year occupation and a system where Palestinians have a different set of rules and don’t get to vote for their own government and face a different legal system than their settler neighbours, that is something that people reject and want to see the US work to end.”

But some Democrats who support racial justice causes are nevertheless uneasy with the comparison.

Ron Klein, chair of the Jewish Democratic Council of America, said: “We made it clear to our friends in Black Lives Matter and various civil rights organisations we’re on the same team. The Palestinian issues are a separate set of issues. Don’t conflate the two, they’re totally different, and that is not part of the formal Black Lives Matter movement.”

Klein believes “the Squad’s” recent statements have gone too far. “I think that they’re wrong,” he continued. “They’re entitled to their opinion as elected members of Congress but they’re taking a lot of their information out of context. I’m not here to suggest that Israel always does the right things but Israel is a very strategic ally to the United States.”

Palestinians return to their houses which were destroyed by the Israeli military, in Beit Hanoun, in the northern Gaza Strip, on Friday.
Palestinians return to their houses which were destroyed by the Israeli military, in Beit Hanoun, in the northern Gaza Strip, on Friday. Photograph: APAImages/Rex/Shutterstock

Still, the political and social upheaval of recent years has shaken many old certainties about crossing lines once perceived as uncrossable. Democrats who may have long harboured doubts about Israeli policy, but bit their lip because of assumed political risks, now feel at liberty to speak out.

Peter Beinart, editor-at-large of Jewish Currents, tweeted: “The reason the American debate over Israel-Palestine could shift dramatically and quickly is that many Democratic politicians don’t need to be convinced that what Israel is doing is wrong. They just need to be convinced that they can say so without hurting their careers.”

Biden, who has impressed many young liberals with his bold agenda, finally seems to have run into an issue where old, cautious habits die hard. However, with Democrats holding only narrow majorities in both the House and Senate, “the Squad” might be deterred from causing a serious split over a foreign policy issue when so much is at stake on the home front.

Max Berger, editorial director of the liberal group More Perfect Union, said: “I think it’s very unlikely that this portends any kind of significant rupture in the Democratic coalition but it does open up a question: will the White House be as responsive to progressives on foreign policy as they have been on domestic policy? The honest answer is, we’ll see.”