More than 500 days after Russia launched its invasion of Ukraine, the war loomed over President Joe Biden's weeklong, three-stop trip to Europe.
The summit laid bare some of the existing tension amid allies even while making significant progress in cementing the West's unity against Russia while reasserting America's role in the world more broadly. While Biden returns to Washington delivering some decisive wins, serious questions remain about the trajectory of Russia's invasion, as well as the future of the NATO alliance after the 2024 US presidential election.
Here are five takeaways from Biden's key trip to Europe:
A big win for the alliance as Turkey stands down on Sweden block
NATO members arrived at the summit with a remarkable display of unity after a Monday meeting between NATO Secretary General Jens Stoltenberg, Sweden President Ulf Kristersson and Turkey President Recep Tayyip Erdoğan Monday led to a stunning about-face by Erdoğan, ending his block on Sweden's bid to join NATO.
While some of his lieutenants expressed uncertainty about reaching a resolution on Sweden's future at the summit, Biden projected optimism ahead of the summit and later dismissed "cynicism."
"There was some cynicism about whether I could talk the Turks into Sweden," he noted to reporters Wednesday, continuing a familiar theme of calling on his skeptics to look at his record.
Biden and his top officials were instrumental in getting Erdoğan to yes, leading a full-court press in the days before the summit and making progress on the potential sale of F-16 fighter jets to Ankara.
Finland and Sweden's seats at the NATO table marked a powerful signal of how abruptly the geopolitical landscape has changed, as the two Nordic countries abandoned a strict neutrality policy as war broke out on their doorsteps.
Drama over Ukraine's membership
Ukraine was the top agenda item for NATO leaders in Vilnius, and the discussion of a pathway for the war-torn country to join the alliance prompted division among leaders.
Sweden's moment in the spotlight was soon overtaken as Ukrainian President Volodymyr Zelensky issued a blistering statement on his way to Vilnius on Tuesday, expressing his frustration at not receiving more specific details on when and how Ukraine would join the alliance in the communiqué issued by leaders.
Biden and other top US officials have emphatically stated that Ukraine cannot join the alliance while Russia's war is ongoing, and have also said Ukraine still has reforms to make.
But by Wednesday, leaders had appeared to smooth things over with G7 members unveiling a substantial show of support for Zelensky in a joint declaration of support aimed at bolstering Ukraine's military capabilities.
After meeting with Zelensky for more than an hour, Biden told reporters that he was able to reassure his Ukrainian counterpart.
"The one thing Zelensky understands now is that whether or not he's in NATO now is not relevant as long as he has the commitments," he said.
Biden later said he had a "very good, long meeting with Zelensky, who ended up being very happy."
Still, the trajectory of the war is unclear as the counteroffensive drags on, and there is no concrete timeline for Ukraine's membership.
Biden's vision for America's role
The president presented his vision for America's role in the world as a defender and promoter of democracy, reaffirming his "America's back" refrain to allies as former President Donald Trump's effect appeared to linger on in his conversations. Those questions are only heightened by Trump's continued lead in GOP primary polling.
Biden, who has framed the central challenge of his presidency -- an "inflection point" -- as the fight between democracy and autocracy, continued that contrast at an address on foreign policy in Vilnius on Wednesday evening, using the bully pulpit to highlight his foreign policy experience as he seeks a second term.
He said the world faces a choice "between a world defined by coercion and exploitation, where might makes right, or a world where we recognize that our own success is bound to the success of others, when others do better, we do better as well," Biden said in remarks to a crowd at Vilnius University.
And ahead of the summit on a stop in London, Biden highlighted a US-UK special relationship intact and on full display following the Trump era, meeting with Prime Minister Rishi Sunak for the sixth time in six months and with King Charles III on an issue of mutual concern, climate change.
But nowhere was Trump's shadow more palpable than in Helsinki, where Biden met with Nordic leaders at the same site where, exactly five years ago this week, Trump held a summit with Putin, siding with the Russian leader over the US intelligence community regarding interference in the 2016 election. The 2018 moment rocked Washington and allies across the globe. Thursday in Finland, Biden offered a vastly different tone.
Pressed by a Finnish reporter on political uncertainty in the US and whether allies could be confident in the US' commitment to the alliance even as a change in the White House could come in 2024, Biden declared it ironclad.
"There's overwhelming support from the American people, there's overwhelming support from the members of Congress -- both House and Senate -- both parties, notwithstanding the fact there's some extreme elements of one party. We will stand together," Biden said.
Biden added that the American people "know" that US security "rests in the unanimity among European and transatlantic partner."
"No one can guarantee the future. But this is the best bet anyone could make," he said.
That, of course, could be out of Biden's hands if Trump prevails in 2024. The former president raised the prospect of withdrawing from the alliance multiple times in 2018, The New York Times reported.
China looms
While Ukraine and standing up to Russia's aggression dominated the summit spotlight, China's rising global influence loomed large, with significant statements from the alliance prompting a rebuke from Beijing.
The alliance's communique noted that China's ambitions and policies "challenge our interests, security, and values," calling out its "malicious hybrid and cyber operations" and "confrontational rhetoric and disinformation."
And Stoltenberg voiced concerns that what is happening in Ukraine today could occur in Asia tomorrow.
"The Chinese government's increasingly coercive behavior abroad and repressive policies at home challenge NATO's security, values, and interests," he wrote on the Foreign Affairs website.
China fired back, urging NATO to cease its "groundless accusations and provocative remarks" against the country, Chinese Foreign Ministry spokesperson Wang Wenbin said in a news briefing.
But as NATO and China traded jabs, the reality of that threat presented itself.
China-based hackers have breached email accounts at two-dozen organizations, including some US government agencies, in an apparent spying campaign aimed at acquiring sensitive information, according to statements from Microsoft and the White House late Tuesday.
A strenuous schedule
Close observers of the 80-year-old president's physical fitness and vigor saw Biden keep a rigorous schedule over the trip, which began Sunday morning Eastern Time.
Biden fielded questions from reporters just twice, on the tarmac as he departed Lithuania Wednesday and at a news conference in Helsinki Thursday evening. He also gave a major address, held numerous bilateral meeting and attended two summits.
On Tuesday, Biden skipped a Heads of State and Government dinner at Lithuania's presidential palace, returning to his hotel before the dinner's scheduled start, and refocusing questions on the president's age.
The White House downplayed the absence, saying Biden "has four full days of official business and is preparing for a big speech tomorrow in addition to another day at the summit." But the moment wasn't the first time he has skipped a leaders' dinner abroad. He missed the leaders dinner last November in Indonesia during the G20 Summit, and also departed a G7 dinner last month in Hiroshima early last month to get briefed on debt ceiling negotiations.
Biden, however, sought to frame his age as a source of wisdom and experience.
"I've been doing this a long time. I don't think NATO's ever been stronger," Biden said during his meeting with Finland's President Sauli Niinistö