President Joe Biden on Thursday said the billions of dollars of defense aid he has authorized for Ukraine will strengthen Kyiv’s hand “in future negotiations” as he met with Ukrainian President Volodymyr Zelensky in the Oval Office for what could be the final time during his presidency.

Sitting alongside Zelensky, Biden thanked the Ukrainian leader for sharing his own plan for victory in his country’s nearly three-year-old war against Russian invading forces. He added that it was important “to strengthen Ukraine’s position on the battlefield” by releasing all of the aid approved by Congress in the supplemental defense aid package he signed into law earlier this year. The billions of dollars worth of defense assistance will be delivered to Kyiv before Biden leaves office in January.

He also told Zelensky of the importance of supporting Ukraine’s “long-term” success, including through eventual paths to European Union and NATO membership as well as through ensuring Kyiv retains “sufficient capabilities to against future Russian aggression.”

“I'm proud of the steps we've taken [and] of our partnership on these fronts,” Biden said.

“Earlier this summer, we launched the Ukraine compact with more than 20 nations committed to Ukraine's long-term security, and yesterday, with over 30 nations and the EU, we launched the Joint Declaration of Support for Ukraine's recovery and assets as well... These two elements are critical to how this war ends. Russia will not prevail in war. Russia will not prevail. Ukraine will prevail, and [we] will continue to stand by you every step of the way,” the president added.

For his part, Zelensky thanked Biden once again for his strong support over the course of the war and told the American leader that Ukrainians “deeply appreciate that Ukraine and America have stood side-by-side from the very first moment of this terrible Russian invasion.”

“Your determination is incredibly important for us to prevail,” he said. “We must restore normal life, and we greatly value your leadership, Mr President.”

Zelensky said the $7.9 billion in aid announced by the White House “will be a great help” and revealed that he and the American president were “preparing to discuss the details” and “strengthen” his “plan for victory” over Russia.

The Ukrainian leader also met with Vice President Kamala Harris on Thursday in her ceremonial office in the Eisenhower Executive Office Building, during which Harris — the Democratic presidential nominee — told Zelensky that her support for Kyiv’s defense is “unwavering.”

“I have been proud to stand with Ukraine. I will continue to stand with Ukraine, and I will work to ensure Ukraine prevails in this war, to be safe, secure and prosperous. The United States must continue to fulfill our longstanding role of global leadership,” she said.

“We must stand with our allies and our partners. We must defend our democratic values and stand up to aggressors, and we must stand for international order, rules and norms. Each one of these principles is at stake in Ukraine, and that is why Ukraine’s fight matters,” Harris added.

She warned that allowing Putin and Russia to prevail would embolden the Russian leader to further threaten NATO members such as Poland and the Baltic states.

“We also know that other would-be aggressors around the world are watching to see what happens in Ukraine. If Putin is allowed to win, they will become emboldened, and ... history is so clear in reminding us: the United States cannot and should not isolate ourselves from the rest of the world. Isolation is not insulation,” she said.

In what appeared to be a veiled swipe at former president Donald Trump and his Republican allies, Harris admitted to Zelensky that there are “some” in the US “who would instead force Ukraine to give up large parts of its sovereign territory, who would demand that Ukraine accept neutrality, and would require Ukraine to forgo security relationships with other nations.”

“These proposals are the same of those of Putin, and let us be clear: they are not proposals for peace. Instead, they are proposals for surrender, which is dangerous and unacceptable,” she said.

Zelensky has been in the United States for the UN General Assembly, where on Wednesday he warned world leaders that Russian president Vladimir Putin is attempting to “break the Ukrainian spirit” by targeting his country’s energy infrastructure. He also cautioned against accepting purported peace deals that would be negotiated without Ukraine having a say.

“Any parallel or alternative attempts to seek peace are, in fact, efforts to achieve an out instead of an end to the war,” he said, adding later that he was skeptical of the “true interest” behind a recent push by China and Brazil to foster an end to the conflict.

“When some propose alternatives, half-hearted settlement plans, so-called sets of principles, it not only ignores the interests and suffering of Ukrainians ... it not only ignores reality, but also gives Putin the political space to continue the war,” he said.

Zelensky also toured a Pennsylvania plant where munitions destined for his armed forces are being made. That visit drew anger from Republicans, including House Speaker Mike Johnson, who called for Zelensky to fire the Ukrainian ambassador to the US in response. Johnson’s outrage was supposedly due to no Republicans being invited along to the tour of the plant, though White House spokesperson Karine Jean-Pierre dismissed it as a “political stunt” by the GOP at a press conference on Thursday afternoon.

The sit-downs between Zelensky and the two American leaders come after Biden announced another large tranche of US security assistance for Kyiv. That assistance includes nearly $8 billion in aid from Defense Department and State Department programs, as well as access to Joint Standoff Weapon long-range munitions and additional Patriot anti-aircraft missiles and another Patriot battery.

“Through these actions, my message is clear: The United States will provide Ukraine with the support it needs to win this war,” Biden said in a statement.

The president noted that Ukraine has “won the battle of Kyiv, reclaimed more than half the territory that Russia seized at the start of the war, and safeguarded its sovereignty and independence” during the time that his administration has worked to surge defense aid to the country.

“For nearly three years, the United States has rallied the world to stand with the people of Ukraine as they defend their freedom from Russian aggression, and it has been a top priority of my administration to provide Ukraine with the support it needs to prevail ... but there is more work to do,” Biden added.

Biden’s announcement of more security aid to Kyiv comes just weeks before a US presidential election that could determine whether Ukraine remains a sovereign country or becomes a Russian vassal state. Trump was impeached in late 2019 for using US security aid to attempt to blackmail Zelensky into announcing sham investigations into Biden and his son. Nearly five years later, he has threatened to cut off American assistance to Kyiv if he gets a second term, all while promising to end the war by forcing Zelensky to accept terms that would be favorable to Putin.

Zelensky was set to meet with Trump in New York, but it was initially canceled. Now, Trump said on Thursday that he plans to meet with the Ukrainian leader on Friday.