Updated May 21, 2021 at 7:34 PM ET

For decades, Democrats and Republicans alike have stood by Israel, almost unconditionally, insisting the country has a right to defend itself.

President Biden did that throughout the recent conflict as Hamas militants fired thousands of rockets into Israel. Now, Biden has pledged to help replenish Israel's air defense system while promising humanitarian aid to Gaza, which was pounded by fierce Israeli airstrikes before a cease-fire took effect early Friday.

But this latest violence marked a shift in the American political debate over Israel. The criticism from the left was louder than in the past, with progressives pressuring Biden to speak up forcefully in support of Palestinians, who saw a far greater civilian death toll in recent days.

This shift is tied to two main factors: the growing power of racial justice movements in the United States and Israeli Prime Minister Benjamin Netanyahu's embrace of the American right wing in recent years.

Those forces sparked the biggest public disagreement yet between Biden and the progressive wing of his party. To some, news of a cease-fire was welcome but insufficient; they want the Democratic Party to rethink its relationship fundamentally with Israel.

"This cease-fire does not change the fact that so many have died and the U.S. has been complicit in this violence," Varshini Prakash, executive director of Sunrise Movement, said in a statement. "Biden and Congress can't call for a cease-fire while continuing to hand over the very weapons responsible for trapping and killing innocent children."

The Sunrise Movement, a youth-led climate change organization, was one of 140 progressive groups that signed a statement last week calling for the Biden administration to condemn the Israeli government's plans to "forcibly displace Palestinians."

"It's just simply a fact that there was never this kind of pressure vocally from the left on issues related to Israel during the Obama years," said Ben Rhodes, a former deputy national security adviser in the Obama administration.

"There's now just a much wider spectrum of opinion in the party," he added. "And therefore it's going to be harder to just stick to the old line of essentially unquestioned support for the policies of the Israeli government."

The Biden administration knew its decision to not call for an immediate cease-fire would receive tremendous pressure from progressives, but it felt that a more behind-the-scenes approach would avoid the kind of protracted war the world witnessed in 2014.

A number of current White House officials were working in the Obama administration during the 2014 Israeli-Palestinian conflict, and they wanted a different approach this time.

Biden was asked about that approach on Friday and whether he felt pressured by emerging skepticism from the left to take a more confrontational approach to Israel. He responded: "There is no shift in my commitment — the commitment to the security of Israel. Period. No shift, not at all."

Going a step further, he added: "I think that my party still supports Israel. Let's get something straight here. Until the region says unequivocally they acknowledge the right of Israel to exist as an independent Jewish state, there will be no peace."

The link to Black Lives Matter activism

Young activists see the Israeli-Palestinian conflict as a power struggle, akin to the movement for Black lives.

"Our generation doesn't view issues through a single-issue lens," said Evan Weber, political director of the Sunrise Movement. "We have grown up participating in social movements that have been sweeping the country."

And, like racial justice movements in the United States, activists said social media have helped shift the narrative around the Israeli-Palestinian conflict.

"One of the major things that's different about this moment is access to information," said Rahna Epting, executive director of the progressive group MoveOn, which also signed that joint statement by progressive groups. "We are seeing videos of fathers holding their dead daughters. And we're seeing reports directly from Palestinians for probably the first time."

In recent years, activists have helped elect a new generation of progressive politicians, such as Rep. Rashida Tlaib, D-Mich., the first Palestinian American woman in Congress, and Rep. Cori Bush, D-Mo., a Black Lives Matter organizer elected last year.

In turn, they are changing the conversation in Congress.

"Palestinians are being told the same thing as Black folks in America: There is no acceptable form of resistance," Rep. Ayanna Pressley, D-Mass., said in a speech on the House floor.

Progressives in Congress and on the street often compare the Palestinian cause to fights for racial justice in America.

That comparison is the result of years of intentional efforts at creating Black-Palestinian solidarity. After the 2012 killing of Trayvon Martin, a 17-year-old Black teenager in Florida, Ahmad Abuznaid co-founded a group called Dream Defenders that organizes Black and brown communities.

"In 2012, on our first march — we were marching to Sanford, Fla., where Trayvon was killed. And on that march, I was wearing a kaffiyeh, the Palestinian scarf that many rightly identify with the Palestinian struggle, and we had conversations about state-sanctioned violence," Abuznaid said.

Through Dream Defenders, he went on to lead four delegations of Black activists, that included people such as Patrisse Cullors, one of the co-founders of the Black Lives Matter movement, to Israel to see how Palestinians live.

Israeli politics and American polarization

This shift though is not entirely about domestic U.S. politics, with analysts, activists and operatives saying it's also tied to Israeli politics.

"Prime Minister Netanyahu really made the strategic decision for Israel to throw in the country's lot with the Republican Party and with the right wing," said Jeremy Ben-Ami, president of the liberal Jewish lobby J Street.

Netanyahu famously came to Washington in 2015 at the invitation of Republicans and gave a speech to Congress blasting a signature foreign policy goal of the Obama administration: the Iran nuclear deal.

Democrats say that under former President Donald Trump most issues became more polarized, and Israel was no exception. Ben-Ami said the right tried to box Democrats in.

"You were either 'with us or against us' and anybody who supported two states, who recognized Palestinian rights, who wanted peace was anti-Israel," he said.

Rhodes said Democrats are also dealing with a different reality on the ground.

"There's kind of an old set of talking points in the Democratic Party where you're basically expressing full support to Israel but also saying you do support a two-state solution," Rhodes said. "And, I think people can see that those talking points don't work anymore — that the circumstance around a two-state solution has deteriorated to the point that it's hard to credibly say we stand with no daylight with the Israeli government, but we also stand for Palestinian rights."

And so left-wing Democrats are trying to force their party to pick a side.

Part of the frustration for progressives is that they feel they've been able to nudge the president on other issues, such as climate change or racial justice, but not on this one.

"It's been very disappointing," said Weber with the Sunrise Movement. "I think it's been one of the most disappointing things we've seen from the Biden administration."

This push from the left, however, is not without controversy. When the chair of the Nevada state Democratic Party put out a statement last week saying the U.S. "has for too long turned a blind eye to injustice and violence committed by the Israeli government, dominated by the extreme right wing," her comments drew sharp criticism from multiple members of Nevada's congressional delegation. The state party's treasurer resigned his position because of the statement, and a Jewish group accused the chairwoman of using "inflammatory" and "biased" language.

It may be unlikely the left will transform conventional Democratic foreign policy around Israel, but it will continue to prod Biden. A cease-fire is not enough, activists said. Progressives are also protesting a $735 million arms sale to Israel.

NPR Politics reporter Alana Wise contributed to this report.

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