President Volodymyr Zelensky of Ukraine canceled plans on Tuesday to make a direct, last-ditch appeal to senators for tens of billions more in emergency military aid for his nation, a day before a critical Senate vote that was expected to show growing opposition in Congress for continuing to fund the war effort.
Mr. Zelensky had planned to speak to senators in a classified briefing via confidential video call, arranged at the behest of Biden administration officials. His remarks were orchestrated as part of an urgent effort by Democrats and the White House to wear down Republican resistance to a bill that would provide more than $61 billion as Ukraine tries to repel an invasion by President Vladimir V. Putin’s Russia.
“Something happened at the last minute,” Senator Chuck Schumer of New York, the majority leader, said on Tuesday afternoon, announcing the change in plans, without giving further explanation.
Earlier on Tuesday, he had heralded Mr. Zelensky’s planned appearance as an important message to Republicans, who have resisted more funds for Ukraine unless Congress simultaneously adopts policies to clamp down on migration at the U.S. border with Mexico, which Democrats have rejected.
“The last time he spoke to us, his message was direct and unsparing: Without more aid from Congress, Ukraine does not have the means to defeat Vladimir Putin,” Mr. Schumer said of Mr. Zelensky on the Senate floor Tuesday morning. “Those who think Vladimir Putin will stop merely at Ukraine willfully ignore the clear and unmistakable warnings of history. It is therefore urgent for the Senate to pass a security supplemental.”
The Senate is set to take a critical test vote on the legislation on Wednesday, despite Republican pledges to block the measure. Mr. Schumer tried to curry G.O.P. support for the bill by offering Republicans a vote on a border amendment of their choosing, if they helped advance the measure. But Republicans remained firm in their opposition, all but guaranteeing the vote would spotlight flagging U.S. resolve at a critical time in the war.
“I hope all of our members vote no,” Senator Mitch McConnell of Kentucky, the minority leader, told reporters on Tuesday. Mr. McConnell has been the G.O.P.’s most outspoken proponent of continuing to arm Ukraine, but he said his opposition to the bill was “to make the point, hopefully for the final time, that we insist on meaningful changes to the border.”
The vote, coming just days after the White House warned that the United States would soon run out of money to send weapons to Ukraine, comes at perhaps the most uncertain moment for the beleaguered nation since the first chaotic months of the war.
Ukraine urgently needs more ammunition and other weapons to try to turn the tide on the battlefield. The country’s counteroffensive against entrenched Russian forces in southern Ukraine has so far failed to meet its objectives, and Moscow’s forces have been going on the offensive in the east.
But Republican leaders have been unmoved by warnings from Democrats and the White House. Instead, they have insisted that if the Biden administration wants speed aid to Ukraine, they must meet the G.O.P.’s demands for border security measures and a clearer strategy for resolving the war.
“Rather than engaging with congressional Republicans to discuss logical reforms, the Biden administration has ignored reality, choosing instead to engage in political posturing,” Mike Johnson, the House speaker, wrote in a letter on Tuesday to Shalanda D. Young, the director of the White House Office of Management and Budget. He was responding to a letter Ms. Young sent congressional leaders on Monday warning that the U.S. coffers for Ukraine were about to run dry.
“Supplemental Ukraine funding is dependent upon enactment of transformative change to our nation’s border security laws,” Mr. Johnson said, adding that the administration also must provide lawmakers with specifics about how the assistance to Ukraine was being used.
Mr. Johnson, who has repeatedly voted against aid to Ukraine, has insisted that any assistance to Ukraine be coupled with legislation passed by the House this year that would reinstitute severe Trump-era immigration policies.
Ukrainian officials are familiar with the challenges of getting assistance through Congress. Republicans have twice refused to include military aid for Ukraine in stopgap spending bills to keep the government funded this autumn.
Mr. Zelensky’s speech was intended to be the cornerstone of a broader lobbying effort in which Ukrainian officials are making direct appeals to lawmakers to put aside their political differences.
In remarks at the U.S. Institute of Peace in Washington, Andriy Yermak, the head of the presidential office of Ukraine, said on Tuesday that if Congress fails to approve military assistance for Ukraine swiftly, there is a “very high possibility” that Ukraine will lose the war.
It would be “impossible to continue to liberate, and give the big risk to lose this war,” Mr. Yermak said, addressing the audience in English.
The message, however, has been somewhat complicated by conflicting assessments from the Biden administration. Some Pentagon officials have pushed back against claims that military assistance to Ukraine is about to run out, pointing to near-weekly shipments of arms and ammunition worth more than $100 million each. They added that they expected to make the remaining $4.8 billion in aid authority last through the winter.
But Ukrainian officials insist that without an influx of more, they are doomed at best to a stalemate. As weapons shipments have slowed, Ukrainian troops have struggled to advance on the battlefield — and are also facing recruitment and training challenges as the loss of soldiers mounts.
The warnings being voiced in Washington have been echoed in Ukraine, where officials have for months been making the case for continued military assistance.
The alternative would be “catastrophic,” Mykhailo Podolyak, an adviser to Mr. Zelensky, said on social media on Tuesday.
Mr. Putin has made it clear he is investing in a long war: Nearly a third of the country’s spending next year — roughly $109 billion — will be devoted to “national defense,” according to a budget he signed into law last week.
Mr. Zelensky has repeatedly warned of the risks that dwindling U.S. military assistance would pose while also seeking ways to bolster domestic weapons production. In recent weeks, he has expressed concern that the war between Israel and Hamas in Gaza could distract allies and potentially undermine support for Ukraine.
“Our deliveries have decreased,” Mr. Zelensky told reporters on Nov. 16, referring specifically to 155-millimeter shells, saying “they really slowed down.”
He also has worked to send a clear message to the Biden administration that his government is working hard to tackle issues like corruption — a longstanding issue in Ukraine that some Republicans have pointed to as an argument against further aid.
Mr. Zelensky replaced his defense minister, Oleksii Reznikov, in September amid accusations of embezzlement in military procurement. Later that month, the White House gave Ukraine a list of “priority reforms” to undertake — namely shoring up anticorruption efforts — that suggested future aid would be linked to implementing the changes.
Some of those efforts were on public display in Kyiv on Tuesday, where officials held a conference on anti-graft policies in the Ukrainian government called “Integrity: The Future of Ukrainian Society.”
Anastasia Radina, the head of the Anticorruption Committee in Ukraine’s Parliament, was one of about 100 people in attendance. She said there was no risk of corruption around the donation of weapons from allies, describing a bar-code system used to track the arms.
Ms. Radina also said she had visited Washington last month to discuss Ukraine’s anticorruption overhauls with members of Congress.
“I see that the partners are asking us to do the very things the Ukrainian population wants us to do,” she said, adding that “the partners are not asking anything beyond what our own people want.”
Andrew E. Kramer and Eric Schmitt contributed reporting.