Five Senate Democrats on Friday signed onto a measure that would condition aid to Israel on its compliance with international law, bringing the total number of co-sponsors to 18. And a prominent Democrat, Sen. Tim Kaine of Virginia, is rounding up support for his amendment to stop President Biden from circumventing Congress when he orders weapons transfers to Israel, a maneuver the president has pursued twice in recent months.

Earlier this week, 11 senators voted for a bill by Sen. Bernie Sanders aimed at forcing the Biden administration to examine potential human rights abuses by Israel.

After weeks of unquestioning support, the Senate is emerging as a center of resistance to Biden’s unwavering embrace of Israel — at least in modest ways — as even centrist Democrats are signaling their discomfort with the president’s “bear hug” of Israeli Prime Minister Benjamin Netanyahu. A number of prominent Democrats have proposed or backed measures that aim to hold Israel accountable or to shift American strategy, even if they are unlikely to garner enough support to pass.

The growing willingness of establishment Democrats to criticize or push back on Israel — a move that would have come with serious political ramifications just a few months ago — signals a shift in the politics of the party since the war in Gaza began more than 100 days ago. Senators from swing states, including Georgia, Wisconsin and Minnesota, have signed on to some of these measures as polls show a notable drop in support for Biden among young, Muslim and Arab American voters over his handling of the issue.

While few senators are voicing full-throated criticism of Biden’s Israel policy, the new, more skeptical tone reflects an increasing unease as the civilian toll in Gaza rises and Israel repeatedly flouts U.S. requests to modify its military onslaught.

“Every week the Netanyahu coalition promises the Biden administration that we will see meaningful changes, and every week it never materializes,” said Sen. Chris Van Hollen (D-Md.), who, along with Kaine, organized the effort to impose conditions in exchange for aid. Van Hollen noted that some members of Netanyahu’s far-right coalition are even “bragging” about ignoring American requests.

Van Hollen said he initially supported Biden’s embrace of Netanyahu, when the president flew to Israel shortly after the Hamas attacks to show U.S. support for its close ally. On Oct. 7, militants surged across the Gaza border and began hunting down Israeli civilians, killing 1,200 and taking about 250 hostage. Israel has responded with a months-long war that has killed almost 25,000 Palestinians and left dire humanitarian conditions in Gaza.

As Israel fails to transition to the “lower-intensity” phase of operations it long promised, Van Hollen said, the American approach to its ally needs to change.

The once-remote push to condition aid to Israel and other nations on their compliance with international humanitarian law had 18 co-sponsors as of Friday, when five additional Democratic senators signed on. Sen. Elizabeth Warren (D-Mass.) in an interview estimated that about half of the 51 Democratic and independent senators would vote for such a measure on the floor, a striking total for a body where unconditional aid to Israel had been of the few remaining bipartisan certainties.

Some Biden allies on Capitol Hill are questioning the president’s approach in part because Israel continues to rebuff his push to allow in more aid for a desperate and hungry population and because the Israel-Gaza conflict is spilling over into other areas. Among other things, these senators want Biden to more strategically use the American vote on the United Nations Security Council, where the U.S. has vetoed several attempts to formally urge a cease-fire.

Sanders said he appreciates that Biden has repeatedly called on Netanyahu to dramatically scale down Israel’s military operation, but said it’s clear those appeals have not worked.

“You know what? Netanyahu hasn’t done it,” Sanders said. “So I’m not quite sure why we want to give another $10 billion to a right-wing government that ignores the desires of our president and many of us in Congress.”

The U.S. sends $3.3 billion to Israel in security assistance each year, and the Biden administration has requested an additional $14 billion for the country as part of a supplemental funding package that is being negotiated in the Senate.

As a result of Biden’s unwavering support for Israel, the U.S. has in many parts of the world become identified with a military campaign that has displaced more than 80 percent of the Gazan population and created uninhabitable conditions in the enclave. Over the past month, some far-right Israeli government ministers have endorsed the idea of a “voluntary migration” for Palestinians out of Gaza, even as the Biden administration strongly rejects the idea.

Biden advisers held a private meeting this month about how to return some Palestinians to northern Gaza, a notion that many experts said is unrealistic given that much of the northern half of the strip has been reduced to rubble.

Privately, Biden’s frustration with Netanyahu has been growing in recent weeks as Israel has repeatedly ignored his requests. Instead, Netanyahu is using increasingly harsh language to reject the notion of a Palestinian state, which Biden has said must follow the end of the war in Gaza.

“Every territory we pull out from, we get terror — terrible terror — against us,” Netanyahu said at a news conference on Thursday. “It happened in southern Lebanon, it happened in Gaza Strip, and it happened in Judea and Samaria (the West Bank).” Therefore, Netanyahu said, any resolution must include Israeli control over all territory west of the Jordan River.

Acknowledging that this directly contradicts Biden’s position, Netanyahu added, “I speak this truth to our American friends, and I have blocked the attempt to dictate a reality that would have harmed Israel’s security. A prime minister must be able to say ‘no’ when needed, even to our best of friends.”

Biden and Netanyahu spoke Friday for the first time in nearly a month. The prime minister was politically besieged even before the Oct. 7 attacks, and since the catastrophic security lapse, his popularity has plummeted even further, increasing the pressure on him to hold together his far-right coalition or risk losing power.

On Friday, asked by a reporter if a two-state solution was impossible as long as Netanyahu is in office, Biden replied, “No, it’s not.”

He suggested there were options for a Palestinian state that would have restrictions on it. “There are a number of types of two-state solutions. There’s a number of countries that are members of the U.N. that … don’t have their own militaries,” Biden said, adding that “I think there’s ways in which this could work.”

Despite Netanyahu’s increasingly public defiance, Biden is committed to persuading him through private appeals rather than public declarations. There is no serious discussion inside the White House about changing the strategy in any significant way, according to several senior administration officials and outside advisers, speaking on the condition of anonymity to discuss sensitive matters.

Yet Biden allies are increasingly willing to say publicly that the strategy is not working.

“There was this genuine belief that the way you get Bibi Netanyahu to do what you want him to do is you hug him and bank up political goodwill and use that to push him later,” said Tommy Vietor, a former Obama administration aide and co-host of the podcast “Pod Save America.” “But you have to ask yourself: One hundred days later, where are the results?”

White House officials argue that their strategy has in fact produced results. They point to aid trucks that have been able to get into Gaza, which Israel refused to allow for the first several weeks of the war. They note that Israel is drawing down troops in Gaza, though casualties remain high. They cite the opening of Israel’s Kerem Shalom border crossing with Gaza to allow in additional aid.

“All of these things were really driven by President Biden and by the national security team in terms of urging the Israelis to take a different tack than maybe what they would have otherwise done,” White House spokesman John Kirby said this week. “They get to choose what military operations they conduct. We understand that. But as [Secretary of State Antony Blinken] has said many, many times: How they do that matters, and we are talking to them about the ‘how.’ And they have been receptive to those messages.”

Still, several Biden allies voiced bewilderment that the president had continued his tight embrace of Israel. One ally said Biden’s approach had put the administration in a bind, because it is now directly tied to a war effort that is provoking the world’s condemnation but has not achieved its stated aim of destroying Hamas.

“If you back a government whose strategy is not working, you have a choice: You either convince them to try to change the strategy quietly or you do it publicly,” the ally said, requesting anonymity to speak candidly. “Otherwise, you’re going to be stuck identified with a failed strategy.”

Some Democratic lawmakers are also becoming more anxious that the conflict is spiraling into a broader conflagration, particularly with Biden’s decision to launch strikes against Houthi militants in Yemen, who have fired missiles at commercial shipping vessels in the Red Sea, ostensibly in solidarity with the Palestinians. Iran and Pakistan also launched airstrikes inside each other’s countries this week, as Tehran appears emboldened amid the Israel-Gaza war. And U.S. officials are working to dissuade Israel from opening up a front on its northern border with Hezbollah, a militant group allied with Iran.

“What the prime minister of Qatar says, and the leaders of Saudi Arabia say, is the biggest threat to regional stability is the increase in casualties among Palestinians,” said Sen. Peter Welch (D-Vt.). “It’s creating enormous pressure in those communities. So that’s a serious concern, and we’re not getting any response from the Netanyahu government other than, ‘Give us more money.’ ”

Warren said there was initial resistance among Democrats to push for measures that seemed to question Israel because of a sense that they were unlikely to draw more than a handful of votes. When she met with Palestinian leaders from Massachusetts last month about the nascent push to place conditions on U.S. aid to Israel, she expressed her reservations about putting such a measure on the floor.

“I turned to them and I said, ‘Look, I don’t know about pushing a vote. What if I push a vote, and there are only four of us?’ ” Warren said. Such a result, she told the group, could signal to Netanyahu that “96 percent of the U.S. Senate says, ‘Go do whatever you want to do no matter what, and we’re still going be there with you.’”

One of the attendees responded, “But at least we’d know there are four people who care,” she recalled. That conversation — and others like it across the Senate — helped change some senators’ thinking, Warren said.