President Volodymyr Zelensky of Ukraine made a last-minute plea for more U.S. assistance for his country’s war efforts upon his arrival in Washington on Monday, asserting that Russia is the real winner of the stalled negotiations in Congress.

“If there’s anyone inspired by unresolved issues on Capitol Hill, it’s just Putin and his sick clique,” Mr. Zelensky informed national security officials at the National Defense University in Washington.

The remarks served as a message to Congress, even as the likelihood of passing an aid deal has dimmed. This also marked Mr. Zelensky’s initial appeals during a hastily arranged trip to Washington, which also includes meetings with members of Congress and President Biden on Tuesday.

Mr. Zelensky and the White House have argued that supporting Ukraine would safeguard the Western world in the long run by preventing President Vladimir V. Putin of Russia from attempting to seize more of Europe, although polls indicate that the American public has become increasingly skeptical of providing financial assistance to Ukraine.

“America will be more secure if we stand up to Putin’s increasingly aggressive Russia,” Defense Secretary Lloyd J. Austin III stated on Monday, adding that “Putin still believes that he can outlast Ukraine and that he can outlast America. But he is wrong.”

Mr. Biden is hoping that Mr. Zelensky will not only persuade members of Congress to pass a $110.5 billion emergency spending bill that includes aid for Ukraine, but will also emphasize the importance of defending against Russia’s aggression. The visit comes a week after Republicans blocked the package, casting doubt on any future financial assistance for Ukraine.

On Tuesday, the Ukrainian president will first visit Capitol Hill where Senator Chuck Schumer of New York, the majority leader, and Senator Mitch McConnell of Kentucky, the Republican leader, have arranged a closed-door meeting with senators. He is also expected to meet with Speaker Mike Johnson, a spokesman for Mr. Johnson said over the weekend.

Later in the afternoon, he is scheduled to meet with Mr. Biden at the White House and hold a joint news conference.

“This is exactly the right time to have President Zelensky in town to have these discussions,” John F. Kirby, a spokesman for the White House’s National Security Council, stated regarding Mr. Biden’s invitation to host Mr. Zelensky. “I can assure you that he will make it clear to President Zelensky that we’re standing firm on this supplemental request. We absolutely need to get additional funding to support Ukraine.”

Last week, Mr. Zelensky’s chief of staff warned that without the package, Ukraine could lose the war. Mr. Biden and his aides have also warned that refusing to support Ukraine in the coming months could pave the way for a Russian victory.

Republicans, however, have said that any Ukraine aid must be grouped with restrictions on asylum claims at the United States’ southern border and on another program Mr. Biden has relied on to allow Afghans and other refugees to stay in the United States temporarily, according to people familiar with the matter. They have also pushed for the national expansion of a rapid deportation policy.

Democrats, with the support of the White House, have so far signaled support only for some of the restrictions on asylum, including a move that would impose a stricter definition for migrants to meet when they claim they need refuge because they fear persecution in their home countries.

“There’s no way to get it done this week,” said Senator James Lankford, an Oklahoma Republican involved in the negotiations. He said the only question is whether Congress stays in Washington next week and continues deliberating or picks up the talks in early January. “That’s a big unknown at this point.”

Separately, Mr. Biden is also expected to approve another weapons package using existing funds for Ukraine this month, Mr. Kirby said.

Republicans have grown more outspoken with their skepticism as it has become clear that Ukraine has struggled with its counteroffensive against Russia. While the United States has provided tens of billions of dollars in aid, Ukraine’s top military commander, Gen. Valery Zaluzhny, said last month that the war had reached a stalemate, as deadly battles yielded few territorial gains.