Senators raced on Thursday to revive a sweeping emergency national security aid bill for Ukraine and Israel that has stalled yet again on Capitol Hill amid Republican resistance.
Republicans who voted to block the measure on Wednesday were again withholding their support for moving forward with the bill, which includes $60.1 billion for Ukraine, $14.1 billion for Israel and $10 billion in humanitarian aid. They demanded the chance to propose changes, including adding border restrictions — just one day after having blocked a version of the legislation that included a bipartisan package of border restrictions.
Feuding over what modifications to seek, Republicans were huddling behind closed doors in the Capitol on Thursday morning to iron out their disputes.
Senator Chuck Schumer, Democrat of New York and the majority leader, who had planned a quick vote on the foreign aid-only measure on Wednesday, said he hoped it could now take place on Thursday afternoon. The bill would need 60 votes to advance, which would require the support of at least 10 Republicans.
The impasse was the latest manifestation of discord that has roiled the G.O.P. and ground efforts to pass national security spending bills in both chambers of Congress to a standstill, as Republicans clash over how to address international crises without angering their party leader and presumptive presidential nominee, former President Donald J. Trump.
Senate Republicans had initially signaled early Wednesday that they were likely to support moving forward with a clean foreign aid bill without border provisions as long as they had opportunities to propose changes, terms that Mr. Schumer agreed to in principle. Leaders on both sides were optimistic that they would have enough backing to speedily advance the measure.
But by evening, their optimism had given way to confusion, as Republicans devolved into a familiar crouch, torn between rival factions and utterly unable to make a decision about how to proceed. They spent much of Wednesday afternoon and evening squabbling over which amendments to insist on — and some argued privately they should not allow the bill to move forward at all.
Shortly after 7 p.m., Mr. Schumer sent senators home to “give our Republican colleagues the night to figure themselves out,” promising to reconvene the Senate at noon Thursday. But it was unclear whether G.O.P. senators would be able to resolve their differences by then, or anytime soon.
Republican senators are split, with some staunchly supportive of sending a fresh infusion of military aid to help Ukraine fight off a Russian invasion, and those on the right deeply opposed to doing so. And some G.O.P. senators who back the aid are nonetheless concerned that doing so without exacting a price from Democrats would compromise them politically in an election year, given Mr. Trump’s opposition to backing Ukraine’s war effort.
Several Republican senators who are likely to back the bill regardless of whether they are afforded a chance to change it made themselves known on Wednesday afternoon, by supporting a procedural move needed to bring it up. Eight Republicans — Senators Mitch McConnell of Kentucky, the minority leader; Susan M. Collins of Maine; John Kennedy of Louisiana; Jerry Moran of Kansas; Lisa Murkowski of Alaska; Mitt Romney of Utah; Thom Tillis of North Carolina; and Todd Young of Indiana — voted to advance the measure past that early hurdle.
But other Republicans who have championed aid to Ukraine withheld their support. They included Senators Lindsey Graham of South Carolina, John Cornyn of Texas and James Lankford of Oklahoma. Mr. Lankford spent the past four months negotiating a bipartisan deal to pair Ukraine funding with border security measures, a trade-off Republicans had demanded, only to have it rejected by Republicans on Wednesday.
They are expected to be among the senators insisting on amendment votes as a precondition for their support.
“I’m not giving up on the border,” Mr. Graham said in an interview, despite having voted earlier on Wednesday to kill the Ukraine aid and border deal.
Among the border-related amendments being floated by Republicans are a measure reflecting Mr. Lankford’s border deal and a more severe immigration enforcement bill that House Republicans passed last spring.
There were also talks about a bid to revoke or change the Flores settlement agreement, which sets limits on how long children can be held in detention facilities, according to Senate aides who described the discussions on the condition of anonymity because no decision had been made about whether to pursue the proposal.
Democrats also have a wish list of proposed changes to the measure. Nearly 20 Democratic senators, most of them from the left wing of the party, have signed on to an amendment that would require recipients of security aid to use weapons in accordance with U.S. law, international humanitarian law and the laws of armed conflict — and not hamper efforts to send humanitarian aid to civilians. While the measure does not specifically mention Israel, it was inspired by senators’ concerns about that country’s bombardment of the Gaza Strip running afoul of international law.
Carl Hulse contributed reporting.