Another official suggested that Biden’s aside, made in response to a reporter’s question, was less about siding with progressive sentiment and more a window into his private frustrations with Israeli Prime Minister Benjamin Netanyahu.

Biden has long been privately critical of “Bibi,” and he groused to confidants over Thanksgiving that the prime minister could be a challenging partner, according to another of the officials. Biden believed that Netanyahu hasn’t always focused on the hostages and his quip about the aid likely reflected concerns about Netanyahu’s leadership going forward. The remark leaves some strategic ambiguity that the administration might shift on aid down the line — serving as a way for Biden to keep Netanyahu in check.

Still, the White House’s current stance could put the president on a collision course with members of his own party. Senate Democrats on Tuesday met to discuss pressuring the White House on conditionality, with some of Biden’s staunchest allies noting he could use current regulations to restrict aid.

“There are conditions that are already attached to our aid to a wide range of countries,” Sen. Chris Coons (D-Del.), one of the president’s closest friends in Congress, said Tuesday on Fox News. “The conditions that already apply under law are sufficient for this circumstance.”

The headwinds from Biden’s party have only grown in recent weeks.

This month, congressional Democrats first quietly, then publicly came out in support of imposing conditions. Sen. Bernie Sanders (I-Vt.) was first out of the gate, proposing that Israel not get any more weapons until it stops “the indiscriminate bombing” of Gaza and commits to serious peace talks, among other stipulations.

Biden’s comment appears to have made other lawmakers more comfortable to advocate for the once-toxic idea, though many Republicans and Democrats remain opposed to it. “We regularly condition our aid to allies based upon compliance with U.S. law and international law,” Sen. Chris Murphy (D-Conn.), who leads the Senate Foreign Relations Committee’s Middle East panel, told CNN on Sunday. “It’s very consistent with the ways in which we have dispensed aid, especially during wartime, to allies.”

The call for conditions on military support followed an intense push by progressive Democrats to have the administration support a full cease-fire between Israel and Gaza, rather than the temporary pause now in effect to secure the release of Hamas-held hostages.

The administration is using the nearly week-long pause to urge the Israeli government to be more targeted and deliberate when it resumes its ground operations, particularly as it moves into the country’s south, where thousands of civilians have taken shelter, said the first U.S. official.

Biden administration officials have advised Israel from the beginning to moderate its initial invasion plans, with limited success. Israel “adapted their battle plan” significantly to reduce the number of ground troops sent into Gaza in the invasion’s initial stages, the official said.

But Biden’s continued strong support for Israel’s offensive has incensed his left flank, leaving him vulnerable in a tight race against Donald Trump, his expected 2024 Republican rival. Some Democrats in swing states like Michigan say they won’t pull the lever for the president’s reelection because he lost their vote for supporting Israel’s retaliation for Hamas’ Oct. 7 attack — during which the militants killed 1,200 people in Israel and took around 240 hostages.

Indeed, progressives and some mainstream Democrats note there are already arms-transfer regulations requiring the U.S. to curb weapons sales to countries that violate human rights. Some proponents of imposing conditions say that Israel, which has killed more than 14,000 people in Gaza since the war started, has met that threshold.

“If anyone in Washington has broken the taboo of placing conditions on aid to Israel, it has been some of the leading progressives in Congress, not President Biden,” said Guy Ziv, an expert on U.S.-Israel policy at American University.

But even the president’s fleeting openness to aid restrictions highlights the death throes of a Washington taboo, one that leaders from both parties have been loath to break for years. The irony is that Biden, one of the most pro-Israel presidents of the modern era, welcomed a discussion that could eventually rupture the U.S.-Israel relationship if progressives urging conditions get their way.

“Failing to rule [conditions] out is very different than endorsing it, but perhaps it’s a sign of what we may see in the future in a post-Biden era,” Ziv said.

Previous presidents often criticized Israel. George W. Bush called for “an end to the occupation” of Palestinian lands. Barack Obama, with Biden as his No. 2, opposed Israeli settlement expansion in the West Bank. Even Trump, who was closely allied with Netanyahu, considered leveraging the annual $3.8 billion in military aid the U.S. sends to Israel to broker a peace deal — until he was convinced there was “no connection” between the two.

No other commander in chief welcomed, albeit briefly, the idea of putting restrictions on support for Israel like Biden. It’s certainly a change from 2019, when then-candidate Biden called the idea of putting conditions on aid to Israel “absolutely outrageous.”

“It’s a significant and welcome shift,” said Matt Duss, executive vice president at the Center for International Policy and a former Sanders foreign policy adviser. “Hopefully we can get to a point where he acknowledges it’s actually required by law.”

Biden, however, maintains that eschewing the conditions proposal is what has led to dozens of hostages released from Hamas’ clutches and more humanitarian aid to enter Gaza while standing side by side with Israel.

“I don’t think if I started off with that we’d ever gotten to where we are today,” he said Friday in the same address. The U.S. is already sending military supplies to Israel for the war, and the president isn’t looking to insert conditions as a multi-billion Israel, Ukraine, border and Indo-Pacific aid bill winds its way through Congress. CIA Director Bill Burns traveled to Qatar this week to converse with his Israeli and Egyptian counterparts on the hostage issue.

Biden is known for off-the-cuff remarks requiring his staff to clarify his comments, but none of his officials have said that his comments misstated the administration’s Israel policy.

Biden’s team is waiting for this media cycle to pass and go back to what it was already doing: supporting Israel’s goal of defeating Hamas. “He is going to continue to focus on what is going to generate results,” Sullivan, the national security adviser, said Sunday on NBC News’ “Meet the Press” Sunday program. “That’s the course that he’s on.”

Lara Seligman contributed to this report.