The Biden administration's policy toward Gaza has come under increased pressure from Democrats on Capitol Hill. When Congress returns from a two-week recess on Monday, these members will have an opportunity to follow through on the sternly-worded letters and statements they have issued in recent weeks.

Despite an apparent shift in tone following the Israeli strike that killed seven World Central Kitchen staff last week, the Biden administration maintains that Israel is complying with international law — both in its war conduct and in its provision of humanitarian assistance. As a result, Washington continues to send weapons to Tel Aviv unimpeded. In March, The Washington Post reported that the Biden administration had greenlit more than 100 weapons packages for Israel that fell under the $25 million threshold that would necessitate that it notify Congress. Since then, the administration has continued to sign off on weapons packages, including as recently as the day of the strikes that killed the WCK staff.

The Biden administration is also reportedly close to approving an $18 billion arms package to Israel that would include as many as 50 F-15 fighter jets. While the delivery of the jets would not be immediate — one unnamed U.S. official told Al-Jazeera that even if the approval process were completed as soon as possible, the aircraft would not be delivered until 2029 — the announcement of such a large weapons package could provide Congress with a rare opportunity to debate arms transfer policy in public.

The $18 billion package would mark the largest sale to Israel since the start of the war in October.

It is difficult for Congress to block an arms transfer. Any legislative vehicle used to halt the sale would require a veto-proof majority in both chambers. Congress has never successfully blocked a sale under either the Arms Export Control Act or a Joint Resolution of Disapproval.

But a large number of Democratic members have expressed disapproval or concern over continuing to provide Israel with weapons as it prosecutes its war.

On March 11, Sens. Chris Van Hollen (D-Md.), Elizabeth Warren (D-Mass.), Jeff Merkley (D-Ore.), Peter Welch (D-Vt.), Ben Ray Luján (D-N.M.), Bernie Sanders (I-Vt.), Mazie Hirono (D-Hawaii), and Tina Smith (D-Minn.) sent a letter to Biden describing how the Israeli government has interfered with humanitarian operations. The senators reminded the administration that under U.S. law, the president “should not provide military assistance to any country that interferes with U.S. humanitarian assistance.”

In the House, Reps. Mark Pocan (D-Wisc.), Jim McGovern (D-Mass.) and Jan Schakowsky (D-Ill.) circulated a letter last Friday that called on the president to "reconsider [his] recent decision to authorize the transfer of a new arms package to Israel, and to withhold this and any future offensive arms transfers until a full investigation into the airstrike [that killed the WCK staff] is completed." The letter also called on the suspension of weapons transfers if Israel fails to make changes to mitigate civilian harm in Gaza. By the end of the day on Friday, 37 other members had signed on to the letter, including former Speaker of the House Nancy Pelosi (D-Calif.).

The looming debate over the sale of the F-15 package could allow these members the opportunity to follow through on their words. RS reached out to the offices of each of the Senators to see if they would pursue legislation that would halt arms sales to Israel. None responded (though Van Hollen told Politico that he was “strongly considering” a variety of options to place conditions on aid, and Warren said on CNN on Thursday that it was “clear that Congress has a responsibility to act. We have legal tools here. And as I said, we cannot approve the sale of arms to a country that is in violation of our own laws on this.”)

Sanders in January introduced a resolution that would have forced the State Department to issue a report detailing whether Israel was using weapons provided by Washington to commit human rights violations. The resolution failed in the Senate by a vote of 72-11.

As Stephen Semler of Security Policy Reform Institute has documented, all the senators who signed the letter, with the exception of Sanders, voted on March 23 for a spending package that included a total of $3.8 billion in military aid for Israel and cut off all U.S. funding for UNRWA, the U.N. agency which performs vital humanitarian work in Gaza.