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.