Volodymyr Zelenskiy cancelled a planned address to US senators on Tuesday, as the Biden administration urges Congress to approve billions of dollars in support for Ukraine. The Senate majority leader, Chuck Schumer, announced that Zelenskiy would not be able to attend the classified briefing because “something came up at the last minute”. The Ukrainian president had been expected to speak to senators over Zoom on Tuesday afternoon. The news came a day after the White House sent an urgent warning that Kyiv’s war efforts to defend itself from Russia’s invasion may grind to a halt without further US military and economic assistance. Schumer said the administration had invited Zelenskiy to address the senators so they “could hear directly from him precisely what’s at stake”. “If Ukraine falls, Putin will keep on going,” Schumer said on Monday. “Autocrats around the world will be emboldened. Democracy, this grand and noble experiment, will enter an era of decline.” The Biden administration has warned that Ukraine is on the brink of losing critical ground to Russia without another infusion of financial aid from the US. The Senate is expected to hold a procedural vote on a funding package covering Ukraine, Israel, Taiwan and border security as early as Wednesday. Shalanda Young, the White House director of the office of management and budget, said in a letter on Monday: “We are out of money – and nearly out of time.” Joe Biden has sought a nearly $106bn (£84bn) aid package for Ukraine, Israel and other needs, but there is growing Republican scepticism over assistance for Ukraine and even Republicans who support it are insisting on policy changes on the US-Mexico border to halt the flow of migrants as a condition for approval. The House speaker, Republican Mike Johnson, responded to Young’s letter on Tuesday outlining his caucus’s demands on border security and reiterating his position that funding for Israel and Ukraine should not be included in the same bill. “Rather than engaging with congressional Republicans to discuss logical reforms, the Biden administration has ignored reality, choosing instead to engage in political posturing,” Johnson said. “We stand ready and willing to work with the administration on a robust border security package that protects the interests of the American people.” Negotiations over the border security package broke down over the weekend, aides said. The talks are expected to resume this week. The Senate Republican leader, Mitch McConnell, said on Monday that his party was “still at the table”. Congress has already allocated $111bn to assist Ukraine, including $67bn in military procurement funding, $27bn for economic and civil assistance and $10bn for humanitarian aid. Young wrote that all of it, other than about 3% of the military funding, had been depleted by mid-November. The new package proposes an additional $61bn for Ukraine, mainly to buy weapons from the US, $14.3bn for Israel, which includes $10.6bn for weaponry. There is also nearly $14bn for border security, along with aid for the Asia-Pacific region and other US national security provisions. The Biden administration has said it has slowed the pace of some military assistance to Kyiv in recent weeks to try to stretch supplies until Congress approves further funding. “Congress has to decide whether to continue to support the fight for freedom in Ukraine as part of the 50-nation coalition that President Biden has built, or whether Congress will ignore the lessons we’ve learned from history and let Putin prevail,” the US national security adviser, Jake Sullivan, said on Monday. “It is that simple. It is that stark choice, and we hope that Congress on a bipartisan basis will make the right choice.” Meanwhile, the GOP-controlled legislature has passed a standalone assistance package for Israel as it fights the war with Hamas in Gaza, while the White House has maintained that all the priorities must be met. Growing increasingly uneasy about the death toll in the Israel-Hamas war, Biden’s allies in Congress are pushing the administration to have Israel commit to reducing civilian casualties and allowing aid to Gaza before sending more military aid. On Monday, Senator Bernie Sanders said it would be “irresponsible” for the US to send billions in military aid to Israel without such conditions. “What the Netanyahu government is doing is immoral, it is in violation of international law, and the United States should not be complicit in those actions,” Sanders said in a floor speech.