WASHINGTON (AP) — NATO leaders met this week to celebrate the alliance's 75th anniversary under the cloud of deep political uncertainty in its most powerful member — the United States.

But even as questions swirled about President Joe Biden's future and the implications of a possible return to the White House by NATO skeptic Donald Trump, the 32 allies put a brave face on their strength and unity going forward, particularly in relation to Ukraine.

Over three days in Washington, Ukraine, Russia, the threat posed by an increasingly aggressive China and NATO's future dominated the formal summit discussions, although all eyes were on Biden.

He hoped to use the summit as a symbol of his strength as leader of the free world as he struggles to salvage his reelection campaign. Biden is facing growing calls to withdraw after a poor debate performance against Trump last month.

Here are key takeaways from the summit:

Biden gets some slack

Biden stunned the audience at a meeting of the NATO-Ukraine Council on Thursday by referring to Ukrainian President Volodymyr Zelenskyy as Russian President Vladimir Putin before quickly correcting himself.

At his news conference later at the conclusion of the summit, he mistakenly called Vice President Kamala Harris Vice President Trump.

NATO leaders paid great deference to Biden by either ignoring or sidestepping questions about his comportment, appearance and grasp of the issues. They praised his leadership and the achievements that NATO has made during his tenure in the White House, including rallying the allies to oppose Russia's 2022 invasion of Ukraine and the addition of Finland and Sweden as members.

French President Emmanuel Macron and new British Prime Minister Keir Starmer were asked repeatedly about the gaffe but declined to answer directly.

"We can all have a slip of the tongue," Macron said. "It's happened to me. I'm sure it will happen to me again tomorrow, and I'd ask you to be just as kind to me."

Macron said he had a long discussion with Biden during Wednesday's dinner with NATO leaders and heard his discussions in meetings during the summit. He described Biden as "very much on top of things."

"He knows the issues, and around the table, he is amongst those who has the greatest depth of knowledge on these international issues," Macron said.

Starmer, who made his debut on the international stage at the summit, ducked multiple questions about the gaffe, instead praising Biden for his leadership and his preparation in putting an event together to secure solid outcomes for Ukraine.

"I want to look at the substance of what's been achieved over these two days," he said.

Trump looms over the summit

A potential Trump presidency has raised concerns in some European capitals. Trump has repeatedly questioned NATO's relevance, has suggested he might withdraw from the alliance or short of that has threatened not to defend allies who do not meet the 2% defense spending commitments.

Biden said at his news conference that he's the "best qualified person" to ensure that the 32-member transatlantic alliance remains strong and that Ukraine does not fall to Putin.

"Foreign policy has never been his strong point and he seems to have an affinity to people who are authoritarian," Biden said of Trump. "That worries Europe, that worries Poland, and nobody, including the people of Poland, think if (Putin) wins in Ukraine, he's going to stop in Ukraine."

NATO Secretary-General Jens Stoltenberg said he's not concerned about the U.S. commitment to the alliance if Trump is returned to the White House, because it has bipartisan support in Congress and a record number of allies are hitting their goals for military spending.

Trump was asked this week on Fox News Radio whether he wants the U.S. to exit NATO. He answered, "No, I want them to pay their bills."

Zelenskyy, meanwhile, gave a speech to friendly Republicans, including Senate Minority Leader Mitch McConnell, on the sidelines of the summit, saying he hopes the U.S. never leaves NATO.

"I hope that if the people of America will elect President Trump, I hope that his policy with Ukraine will not change," Zelenskyy said in a question-and-answer session with Fox News host Bret Baier after his speech.

Ukraine brings in aid

Although they stopped short of offering Ukraine an invitation to join, the allies affirmed that Ukraine is on an "irreversible path" to NATO membership and pledged to maintain a baseline of roughly $43 billion in annual support to Kyiv as it defends itself from Russia's invasion and attempts to deter future aggression.

There were new pledges of air defense support, including Patriot missile systems and F-16 fighter jets, as well as promises that individual security deals being signed by NATO members with Ukraine constitute a "bridge to NATO." As part of that bridge, NATO agreed to start up a new program to provide reliable military aid and training to Ukraine and help it get ready to join the alliance.

"Ukraine's future is in NATO," the allies said in their joint communique Wednesday.

Zelenskyy embraced the support of allies who have provided substantial new military aid and a path to joining NATO, but he emphatically pushed for the help to arrive faster and for restrictions to be lifted on the use of U.S. weapons to attack military targets inside Russia.

"If we want to win, if we want to prevail, if we want to save our country and to defend it, we need to lift all the limitations," Zelenskyy said alongside Stoltenberg in the final hours of a summit that saw Ukraine receive fresh commitments of weapons to firm up its defense against Russia.

Harsh words for China

NATO leaders have been concerned about China and its increasing aggressiveness for some time. But in a first, they adopted significantly stronger language calling out Beijing for its support of Russia in its war against Ukraine.

The communique labeled China a "decisive enabler" of Russia's war effort, saying Chinese investments and exports of dual-use items are rebuilding Russia's defense industrial sector. That is helping Russia overcome Western sanctions to ramp up the production of weapons for use in Ukraine.

China has opposed NATO's reach into the Indo-Pacific region, saying it hurts Beijing's interests and disrupts peace and stability in the region, said Lin Jian, a Chinese foreign ministry spokesman.

The four Indo-Pacific countries attending the summit — Japan, South Korea, New Zealand and Australia — issued a joint statement to "strongly condemn the illicit military cooperation" between Russia and North Korea, showing how the military alliance and its Pacific partners are forging closer ties to counter what they see as shared security threats.

"We must work even more closely together to preserve peace and protect the rules-based international order," Stoltenberg said when meeting officials of the four Pacific partners. "Our security is not regional. It is global."