WASHINGTON – In a call with Israeli Prime Minister Benjamin Netanyahu on Monday, President Joe Biden "expressed his support for a cease-fire," according to a White House readout of the conversation.

The shift came after 29 Democratic and independent senators issued a joint statement on the issue earlier Monday.

“To prevent any further loss of civilian life and to prevent further escalation of conflict in Israel and the Palestinian territories, we urge an immediate cease-fire,” said the group led by Sen. Jon Ossoff, D-Ga.

At least 200 Palestinians have been killed in a week of airstrikes, including 59 children and 35 women, according to the Gaza Health Ministry. Ten people in Israel, including a 5-year-old boy and a soldier, have been killed in the rocket attacks launched from Gaza toward civilian areas in Israel.

Democrats split on Israel

The deadly violence isn’t just an urgent foreign policy crisis for Biden. It’s also a fraught political debate in Washington, with Democrats increasingly divided over the consistent economic and military support the U.S. has provided Israel since its founding.

"The movement for a more balanced U.S. policy that is pro-Israel, pro-peace, anti-occupation … has grown significantly over the past few years, and it’s become a major force in the Democratic Party," said Logan Bayroff, communications director for J Street, a left-leaning Jewish advocacy group.

Biden is under mounting pressure from progressives to offer stronger support for the Palestinians, who were sidelined during much of the Trump administration.

Tensions among Democrats were heightened Monday after The Washington Post reported that the Biden administration approved $735 million in precision-guided weapons to Israel. Members of Congress were notified of the sale nearly two weeks ago. It makes up just a fraction of the more than $3 billion in annual security assistance the United States sends to Israel.

Sen. Bernie Sanders, I-Vt., and some Democrats have criticized the aid, saying it needs to come with strings attached.

"We can no longer be apologists for the right-wing Netanyahu government and its undemocratic and racist behavior," Sanders wrote in a New York Times opinion piece, saying it's illegal for U.S. aid to support human rights violations.

"For years we have seen a deepening Israeli occupation in the West Bank and East Jerusalem and a continuing blockade on Gaza that make life increasingly intolerable for Palestinians," Sanders wrote.

Bayroff said J Street wants the White House to ensure none of the U.S. security assistance to Israel is used to fund equipment or other items that Israel deploys for settlement expansion, home demolitions or other activities "that are entrenching occupation and making this conflict worse."

Secretary of State Antony Blinken has repeatedly noted that Hamas, which the U.S. considers a terrorist group, is firing rockets at Israeli civilians. He has not given as much rhetorical attention to the spark that ignited the conflict: an effort by Jewish settlers to evict Palestinian families from their homes in East Jerusalem.

Biden's support for a ceasefire on Monday came in a private call with Netanyahu, not a public demand for an end to the violence. And in that conversation, Biden also reiterated his "firm support for Israel’s right to defend itself against indiscriminate rocket attacks," the White House said.

Ilan Goldenberg, who worked on Israeli-Palestinian negotiations at the State Department during the Obama administration, said Israel has become a more partisan issue – in part because of Netanyahu’s full-throated embrace of the GOP and his hostile relations with the White House during the Obama administration.

There is also, he said, a growing and increasingly vocal minority within the Democratic Party that wants the U.S. to play a different role in the conflict.

“It becomes a very tough sort of political balance for the administration to strike for a Democratic administration to strike on an issue that's increasingly divisive inside the party itself.”

He said there is still a very strong pro-Israel contingent in the Democratic Party, but there’s a sense that lawmakers can be pro-Israel and oppose Netanyahu’s aggressive settlement policies, which have squeezed the Palestinians into ever-shrinking territory.

Some Democrats say Biden's handling of the Israel-Gaza conflict undermines his pledge to put human rights at the center of U.S. foreign policy.

"You aren’t prioritizing human rights. You’re siding with an oppressive occupation," Rep. Ilhan Omar, D-Minn., posted in a tweet last week after the White House issued the readout of Biden's call with Netanyahu.

And even some stalwart pro-Israel lawmakers are starting to shift as the death toll spirals with no resolution in sight.

On Friday, Sen. Bob Menendez, D-N.J., chairman of the Senate Foreign Relations Committee, issued a rare condemnation of Israel's attacks on a building that housed the Associated Press and Al-Jazeera.

"I am deeply troubled by reports of Israeli military actions that resulted in the death of innocent civilians in Gaza as well as Israeli targeting of buildings housing international media outlets," Menendez said.

The ideological makeup of the caucus has also shifted in recent years, with newly elected progressives often being more willing to criticize bedrock U.S. policy positions on Israel and the Palestinian territories.

"The Palestinians are an occupied people. They are an oppressed people. Innocent people and children are suffering as America supports the occupation and denies Palestinians freedom," Rep. Jamaal Bowman, D-N.Y., tweeted.

Rep. Cori Bush, D-Mo., explicitly connected the conflict between Israel and Palestinians to issues of police brutality and racial justice in the U.S. "The fight for Black lives and the fight for Palestinian liberation are interconnected. We oppose our money going to fund militarized policing, occupation, and systems of violent oppression and trauma," Bush wrote in a tweet.

In a House floor speech, Rep. Rashida Tlaib, D-Mich., who is Palestinian American, said she was "a reminder to colleagues that Palestinians do indeed exist, that we are human." Tlaib then condemned her colleagues for continuing "unconditional support" for Israel that "has enabled the erasure of Palestinian life."

But many Democrats in Washingtonsee Israel's alliance as crucial to American interests.

"Firing rockets at civilians in Israel is an act of terrorism, period. The latest rocket fire underscores the need for missile defense programs, such as Iron Dome, which protects Israeli civilians – both Arabs and Jews – from the terrorism of Hamas," Rep. Ritchie Torres, D-N.Y., tweeted.

Others also spoke out against the terrorist group.

“Please don’t be fooled by false choices. Israel and Hamas? If I am asked (to choose) between a terrorist organization and our democratic ally, I will stand with Israel every day of the week,” Rep. Ted Deutch, D-Fla., chair of the House Foreign Affairs subcommittee on the Middle East, North Africa, and Global Counterterrorism, said in a floor speech Thursday.