President Joe Biden made his case before the U.N. General Assembly on Tuesday that the world must remain united in defending Ukraine against Russian aggression, warning that no nation can be secure if "we allow Ukraine to be carved up" as he tries to rally support for Kyiv's effort to repel a nearly 19-month-old Russian invasion that has no end in sight.

The U.S. president called on world leaders to not let support for Ukraine diminish, arguing that Russia is counting on countries to grow tired of prolonged conflict in Kyiv which will "allow it to brutalize Ukraine without consequence." Russia alone is standing in the way of a resolution, Biden argued, saying that Moscow's price for peace was "Ukraine's capitulation, Ukraine's territory and Ukraine's children."

"I ask you this: If we abandon the core principles of the United States to appease an aggressor, can any member state in this body feel confident that they are protected?" Biden said in his address. "If we allow Ukraine to be carved up, is the independence of any nation secure?

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He continued: "I'd respectfully suggest the answer is no."

The president's forceful rhetoric on Ukraine appeared aimed not just for a global audience but for Washington, where an increasingly isolationist strain of the Republican Party is jeopardizing the prospects of the U.S. successfully replenishing the steady flow of aid that has gone to Kyiv since the war began in February 2022.

The Biden administration has asked Congress to greenlight an additional $24 billion in security and humanitarian aid to Ukraine, but Republicans who control the House have all but ignored that request as lawmakers scramble to ensure government funding remains flowing beyond the end of September. Animated by the views of former President Donald Trump, a vocal faction of House Republicans remain steadfastly opposed to more Ukraine aid, even as other GOP lawmakers, primarily in the Senate, continue to advocate support for Kyiv to dissuade Russia from spreading its attacks beyond Ukraine's borders.

"We have to stand up to this naked aggression today and deter other would-be aggressors tomorrow," Biden said in his U.N. address. "That's why the United States - together with our allies and partners around the world — will continue to stand with the brave people of Ukraine as they defend their sovereignty and territorial integrity and their freedom."

Other senior members of the Biden administration were making their case on Tuesday, as Defense Secretary Lloyd Austinpushed allied defense leaders in remarks at Ramstein Air Base in Germany to "dig deep" and provide more air defense systems for Ukraine to help the country wage its counteroffensive.

Indeed, the broader message is intended to resonate beyond Moscow and even Capitol Hill. Washington remains on guard against Chinese aggression in the South China Sea, where competing territorial claims have caused tension in the region. Beijing also wants to reunite the mainland with the self-governing island of Taiwan, a goal that raises the prospect of another war.

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During his address, Biden described the partnerships that the U.S. government was fostering around the globe — from Africa to the Indo-Pacific — that he said were creating economic, security and other advancements, even as he stressed that those relationships were not about "containing any country" — a clear reference to Beijing.

"When it comes to China, let me be clear and consistent," Biden said. "We seek to responsibly manage competition between our countries so it does not tip into conflict. I've said we are for de-risking — not decoupling — with China."

Biden emphasized that Beijing and Washington need to cooperate on climate, and referenced recent natural disasters — devastating heat waves, droughts and floods around the globe — as part of a "snapshot" that tells the "urgent story of what awaits us if we fail to reduce our dependence on fossil fuels and begin to climate-proof the world."

Despite his own emphasis on climate as a priority, Biden does not plan to attend a special summit on climate that U.N. Secretary-General António Guterres will host on Wednesday, where countries are encouraged to bring new ideas and proposals on how to further cut emissions and combat climate change. Officials played down Biden's absence at the climate summit, and said John Kerry, the U.S. climate envoy, will attend in Biden's place.

In his 30-minute address, Biden also repeatedly emphasized the value of institutions such as the United Nations and international coalitions that has helped the world confront significant challenges such as poverty and disease, as well as echoing his defense of democracy, a common theme of his presidency.

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"We will not retreat from the values that make us strong," Biden said. "We will defend democracy — our best tool to meet the challenges that we face around the world. And we're working to show how democracy can deliver in ways that matter to people's lives."

The annual forum was a chance for Biden to showcase to other world leaders — and the 2024 U.S. electorate — that he's reestablished U.S. leadership on the world stage that he says was diminished under Trump.

There were some notable absences as Biden addressed the General Assembly: British Prime Rishi Sunak, French President Emmanuel Macron, Chinese President Xi Jinping and Putin — the leaders of the other permanent members of the U.N. Security Council — are all skipping the gathering. U.S. officials downplayed that fact and instead emphasized the importance that Biden attaches to showing up at the annual diplomatic forum.

For Biden, the more important audience for Tuesday's speech could be closer to home as he looks to make the case to voters that he's skillfully handled a complicated foreign policy agenda and that the experience that comes with age has proved to be an asset. It's an argument that the 80-year-old Biden is likely to continue to make to counter skepticism — even in his own Democratic Party — among voters who are concerned about his age.

After the speech, Biden sat down with Guterres, and later Tuesday met with leaders from the so-called C5 group of Central Asian nations, which include Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan. Saying the cooperation among the nations is at "new heights," Biden outlined several areas of collaboration including on critical minerals and disability rights.

Xi has stepped up his own courting of those countries. During his own summit in May with the Central Asian leaders, Xi promised to build more railway and other trade links with the region and proposed jointly developing oil and gas sources.

"We are stronger, and I genuinely believe the world is safer, when we stand together, our five nations," Biden said following the closed-door meeting with the leaders.

Biden is scheduled to host talks Thursday at the White House with Ukraine President Volodymyr Zelenskyy.