WASHINGTON — Ukrainian President Volodymyr Zelenskyy huddled with U.S. leaders on Thursday to shore up American support for his country's fight against Russia as the war faces a partisan reckoning in this year’s presidential election.

Vice President Kamala Harris, the Democratic nominee for president, has pledged to continue sending military assistance to Ukraine if she's elected. She'll have her own meeting with Zelenskyy after the Ukrainian leader sat down with President Joe Biden, who announced billions of dollars more in missiles, drones, ammunition and other supplies. The weapons include an additional Patriot missile defense battery and a new shipment of glide bombs that can be deployed from Western fighter jets, increasing their strike range.

Biden pledged to ensure that all approved funding is disbursed before he leaves office, and he said he plans to convene a meeting with other world leaders focused on Ukraine’s defense during a visit to Germany next month.

“We stand with Ukraine, now and in the future,” Biden said alongside Zelenskyy in the Oval Office. “Russia will not prevail. Ukraine will prevail.”

Meanwhile, Zelenskyy’s tumultuous relationship with former President Donald Trump, the Republican nominee, continued to deteriorate this week. Instead of meeting with Zelenskyy, Trump criticized him. As for U.S. support for Ukraine, Trump complained that “we continue to give billions of dollars to a man who refuses to make a deal” to end the war. His message dovetails with Russian propaganda that claims intransigence by Kyiv — not aggression from Moscow — has prolonged the bloodshed.

It’s the most politically treacherous landscape that Zelenskyy has encountered in Washington since Russia invaded nearly three years ago. Ukrainian officials are anxious to maintain good relations with whomever becomes the next president of the United States, which is its biggest and most important provider of arms, money and other support.

But the effort risks slipping into the political blender of the presidential campaign, polarizing the discussion around a war that used to be a bipartisan cause célèbre in Washington. About two thirds of Democrats and Democratic-leaning independents said the U.S. has a responsibility to help Ukraine, compared with one third of Republicans and Republican-leaning independents, according to a Pew Research Center poll conducted in July.

Americans are also split on which presidential candidate would do a better job handling the war. An AP-NORC poll from August found that about one-third of Americans said they trusted Harris more, while a similar share said the same about Trump.

Zelenskyy was expected to present Biden with a plan to push the war toward an endgame that would involve a negotiated settlement with Russia. He's trying to secure leverage before Biden leaves office — including acquiescence to fire long-range Western weapons deeper into Russia — as a hedge against the possibility that American support erodes after the election.

On Thursday, Zelenskyy found some bipartisan support as he visited Capitol Hill, where he was greeted by Senate Majority Leader Chuck Schumer and Senate Minority Leader Mitch McConnell.

Sen. Lindsay Graham, a South Carolina Republican, said Zelenskyy asked to use long-range weapons, such as British-supplied Storm Shadow missiles or U.S.-made ATACMS, for “maximum benefit to bring (Russian President Vladimir) Putin to the table” and increase Ukraine's negotiating position.

“If we don’t make that fundamental choice this week, I think the outcome for Ukraine is dire,” Graham said.

Administration officials have been skeptical of Zelenskyy's request, believing the weapons could have limited benefits but increase the risk of escalating the conflict. Sen. Richard Blumenthal, a Connecticut Democrat, said senators gave Zelenskyy advice on how to persuade Biden to loosen restrictions.

Rep. Jim Himes, another Connecticut Democrat and the ranking member of the House Permanent Select Committee on Intelligence, said Zelenskyy wanted “more, faster.”

“He was politely frustrated,” Himes said, and specifically requested more Patriot missile defenses as Russia escalates strikes on Ukraine's cities and energy grid before the winter.

Despite support from some Republicans on Capitol Hill, Zelenskyy faces a much more tense situation with Trump. The latest round of sniping started on Sunday, when The New Yorker published an interview with Zelenskyy in which he criticized JD Vance, Trump's running mate, as “too radical” for suggesting that Ukraine needs to give up some territory to end the war. Zelenskyy also dismissed Trump's boasts that he could quickly negotiate a solution, saying “my feeling is that Trump doesn’t really know how to stop the war even if he might think he knows how.”

On the same day, Zelenskyy toured a Pennsylvania factory producing munitions for the war. He was joined by Democratic Gov. Josh Shapiro, a top surrogate for Harris, and Republicans criticized the visit as a political stunt in a political battleground state.

House Speaker Mike Johnson demanded that Zelenskyy fire the Ukrainian ambassador to the U.S., alleging that the tour was “designed to help Democrats and is clearly election interference.” The Louisiana Republican didn't attend any of lawmakers' meetings with Zelenskyy on Thursday.

Max Bergmann, director of the Europe, Russia and Eurasia program at the Center for Strategic and International Studies, said Zelenskyy is in a “no-win situation” where he “can’t even visit a U.S. weapons manufacturer to say thank you without being attacked.”

Zelenskyy's trip to Washington coincides with the annual meeting of the U.N. General Assembly in New York, where the Ukrainian leader spoke on Wednesday. Last week, Trump said he would “probably” meet with Zelenskyy while he was in the U.S., but a senior campaign official said there was never a meeting on the books.

The official, who requested anonymity to discuss private conversations, said Trump had told Zelenskyy back in July that it would probably be better not to sit down together until after the election. A Zelenskyy aide did not respond to questions about the potential meeting.

Trump was impeached during his first term over asking Zelenskyy for help investigating Biden, then a candidate for the Democratic presidential nomination, at a time when the Ukrainian leader was seeking support from Washington.

Now there are fears that Trump would cut off or add strings to U.S. military assistance if he returned to the White House. Trump has also spoken admiringly about Putin, and this week he praised Russia's record of winning wars.

Charles Kupchan, a senior fellow at the Council on Foreign Relations, said Trump is not wrong to want a negotiated end to the war. However, he said, Trump risks undermining Ukraine by enabling Putin to make more gains on the battlefield.

“Neither Ukraine nor Russia is going to win this war, and the sooner that the parties try to end this, the better,” Kupchan said. “Where Trump goes off course, and where Biden and Harris have a much stronger argument, is that we get to that point not by throwing Ukraine under the bus but by giving them sufficient support so they can block further Russian aggression.”

Zelenskyy can expect a far different tone from Harris, who met with him in Munich just days before Russia invaded.

During her debate with Trump earlier this month, Harris expressed pride in U.S. support for Ukraine's “righteous defense.”

“If Donald Trump were president, Putin would be sitting in Kyiv right now,” she said.