The precise details of the "victory plan" Zelensky plans to present in separate meetings to President Joe Biden and Vice President Kamala Harris are unknown, having been closely held until they are presented to the American leaders.
But according to people briefed on its broad contours, the plan reflects the Ukrainian leader's urgent appeals for more immediate help countering Russia's invasion. Zelensky is also poised to push for long-term security guarantees that could withstand changes in American leadership ahead of what is widely expected to be a close presidential election between Harris and former President Donald Trump.
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The plan, people familiar with it said, acts as Zelensky's response to growing war weariness even among his staunchest of western allies. It will make the case that Ukraine can still win - and does not need to cede Russian-seized territory for the fighting to end - if enough assistance is rushed in.
Ahead of Zelensky's arrival, Biden ordered a surge of assistance to Ukraine, directing the Pentagon to allocate all remaining funding already approved by Congress before he leaves office in the hopes of positioning Kyiv for victory no matter the winner of November's US presidential election.
Speaking to reporters next to Zelensky just before the pair met privately in the Oval Office, Biden said "This will strengthen Ukraine's position in future negotiations."
On post-war recovery efforts, Biden said the US and allies "have to support Ukraine on its path to membership to both the EU and to NATO, and to continue to make reforms to counter corruption," while ensuring the country is able to repel any future Russian attacks.
And he pledged continued US support for recovery and reconstruction efforts in the country, in some cases "using Russian assets as well."
Biden earlier said he was approving new long-range weapons, Patriot missiles and training for fighter pilots, and plans to convene Western leaders next month in Germany to coordinate their efforts toward helping Ukraine achieve victory.
Whether that is enough to help defeat Russia remains to be seen. And, at least publicly, Biden has stopped short of granting Ukraine permission to fire Western provided long-range weapons deeper into Russian territory, a line Biden once was loathe to cross but which he's recently appeared more open to as he has come under growing pressure to relent.
Even if Biden decides to allow the long-range fires, it's unclear whether the change in policy would be announced publicly.
Biden is usually apt to take his time making decisions about providing Ukraine new capabilities. But with November's election potentially portending a major change in American approach to the war if Trump were to win, Ukrainian officials - and many American ones - believe there is little time to waste.
Trump has claimed he will be able to "settle" the war upon taking office and has suggested he'll end US support for Kyiv's war effort.
"Those cities are gone, they're gone, and we continue to give billions of dollars to a man who refused to make a deal, Zelensky. There was no deal that he could have made that wouldn't have been better than the situation you have right now. You have a country that has been obliterated, not possible to be rebuilt," Trump said during a campaign speech in Mint Hill, North Carolina, on Wednesday.
Comments like those lent new weight to Thursday's Oval Office talks, according to American and European officials, who have described an imperative to surge assistance to Ukraine while Biden is still in office.
The president said ahead of his meeting with Zelensky Thursday he was directing the Department of Defense "to allocate all of its remaining security assistance funding that has been appropriated for Ukraine by the end of my term in office."
Biden said he'd decided to provide Ukraine with a Joint Standoff Weapon (JSOW) long-range munition to "enhance Ukraine's long-range strike capabilities," though his statement did not specify whether he planned to lift restrictions on firing the long range weapons deep inside Russian territory.
He also said the Pentagon would refurbish an additional Patriot air defense battery for Ukraine and provide the country with additional Patriot missiles.
The US military will also expand training for Ukrainian F-16 pilots, taking on an additional 18 pilots next year.
The president previewed Zelensky's visit to the White House a day beforehand, declaring on the margins of the United Nations General Assembly his administration was "determined to ensure that Ukraine has what it needs to prevail in fight for survival."
"Tomorrow, I will announce a series of actions to accelerate support for Ukraine's military - but we know Ukraine's future victory is about more than what happens on the battlefield, it's also about what Ukrainians do make the most of a free and independent future, which so many have sacrificed so much for," he said.
Anxiety over the future of American support has colored many of Zelensky's visits to Washington. When he visited the White House last year, it was meant in part to apply pressure on Republican Congressional leaders to approve billions of dollars in new assistance.
The aid was eventually passed, but support for Ukraine among allies of Trump is not high. While Zelensky visited Capitol Hill on Thursday, he did not meet Republican House Speaker Mike Johnson.
During his more than hour-long meeting with senators before his visit to the White House, Zelensky made his case for increased US support for his war-weary country while laying out the plan he would later present to Biden.
Zelensky was emphatic he needs permission to strike deeper into Russia - which many senators on Capitol Hill have supported and something that continues to be a major priorityfor Ukraine.
Some lawmakers in the meeting said they also lent Zelensky some suggestions on how he could be more persuasive with Biden.
Looking to develop relationship with Harris
Zelensky's separate meeting with Harris on Thursday - which will take place after the Ukrainian leader wraps up with Biden - signaled his desire to further develop what would be his most important leader-to-leader relationship should she win.
In the weeks since taking the political baton from Biden, Harris and her aides have gone to great lengths to insist that on major matters of foreign policy, there is no daylight between the vice president and the outgoing president.
The ongoing war between Ukraine and Russia is no exception, they say, insisting that Ukraine would continue to have the US's unwavering support against Russian aggression under a Harris presidency.
The vice president's face time with Zelensky on Thursday would mark their sixth meeting since the war broke out in February of 2022. Just several days prior to the start of Russian attacks in February 2022, the vice president also saw Zelensky at the Munich Security Conference, where the two discussed Russia's military build-up around Ukraine and the possibility of the start of a war.
In her remarks at the Democratic National Convention last month, Harris was deliberate in taking credit for the US's response.
"Five days before Russia attacked Ukraine, I met with President Zelensky to warn him about Russia's plan to invade. I helped mobilize a global response - over 50 countries - to defend against Putin's aggression," she said. "And as president, I will stand strong with Ukraine and our NATO allies."
Advisers to the vice president say Trump's public statements about the war in Ukraine could not make more clear the starkly different foreign policy worldviews of the vice president and the former president. (Trump appears unlikely to sit down with the Ukrainian leader, despite saying last week they would "probably" meet.)
Still, when Harris meets with Zelensky in Washington on Thursday, she does not plan to mention Trump by name in her public remarks, multiple sources familiar said - a move meant to steer clear of any explicit mention of US politics ahead of a somber meeting with the wartime president.
However, those sources said, the vice president's brief remarks will be aimed at laying out what she sees as a black-and-white difference in how she and the former president each views the situation in Ukraine - including America's role in helping Ukraine defend itself from Russian aggression.
Harris has insisted that if she were to become president - unlike under Trump's watch - Ukraine would be able to count on unwavering US support.
Trump's campaign has been blasting Zelensky over an interview with the New Yorker published Sunday in which Zelensky called vice presidential nominee JD Vance "too radical."
"His message seems to be that Ukraine must make a sacrifice. This brings us back to the question of the cost and who shoulders it. The idea that the world should end this war at Ukraine's expense is unacceptable," Zelensky said in the interview. "For us, these are dangerous signals, coming as they do from a potential Vice-President."
Trump alluded to the comments in North Carolina on Wednesday.
"The President of Ukraine is in our country. He's making nasty little aspersions toward your favorite president, me," he said.
There is quiet recognition even inside the Biden administration that any reassurances Zelensky may receive from Biden and Harris this week on the US's commitment to supporting Ukraine could all be for naught under a different American president.
At the signing of a new US-Ukraine defense pact on the sidelines of the G7 meeting in Italy in June, Zelensky was asked what contingency plan he might have for precisely such a scenario.
"If the people are with us, any leader will be with us in this struggle for freedom," Zelensky responded.
CNN's Michael Williams, Lauren Fox, Morgan Rimmer, Ted Barrett, Donald Judd and Sarah Davis contributed.
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