The United States hosted NATO's 75th anniversary summit at a tumultuous time. While Russia's constant attacks on Ukraine continue to have the military alliance on high alert, the host country's leader also finds himself in a precarious position.

Ever since his disastrous debate performance against likely Republican presidential nominee Donald Trump, President Joe Biden has been facing a growing number of calls from within his own party to withdraw his candidacy for another four years in office.

Though Biden himself has insisted he will run in the US presidential election this November, the insecurity surrounding US leadership could be felt among NATO members at the summit in Washington, DC, experts said — especially since Trump is not seen as a source of stability for NATO either.

"One presidential candidate expresses grave doubts about the alliance's value to Americans. The other faces questions in his own party about the continued viability of his candidacy," said Richard Fontaine, chief executive officer of the Center for a New American Security (CNAS), an independent US think tank focused on national security and defense policy. "The allies bring to Washington not only a commitment to Ukraine, but also worries about politics in the alliance's indispensable linchpin."

An 'unfortunate discussion'

Publicly, those attending the summit did not express any doubt about Biden's ability to do his job and to run again in November. Germany's Chancellor Olaf Scholz said before leaving for Washington that he was not worried about Biden's health.

"From the many conversations I have had with the American president, I know that he has prepared this summit very well and very precisely, together with us," Scholz told reporters on Tuesday.

Christoph Heusgen, a top German diplomat who has served as chairman of the Munich Security Conference since 2022, told DW in Washington that the questions swirling around Biden's fitness for office were an "unfortunate discussion."

"The world looks at the US, and to have this debate right now is not helpful. We need ... a strong US leadership," Heusgen said on Thursday. "I just hope this discussion will soon be ended."

Outgoing NATO Secretary General Jens Stoltenberg told reporters that he would not comment on the health of the US president.

"One of the reasons why NATO is successful is that we have always stayed out of domestic political issues," he said at a presummit press conference in Brussels.

Allies' diminished confidence

Experts say there may be some concerns behind the scenes.

"Privately, leaders will be wondering" about the state of Biden's health, Cathryn Clüver Ashbrook, a trans-Atlantic expert with the German Bertelsmann Foundation, told DW. She said NATO members weren't just relying on "hope and optimism" that Biden could do the job and beat Trump anymore, but wanted to be prepared no matter who ends up in the White House come January.   

One sign of that: Members of several NATO delegations met with former Trump administration officials and Republicans close to Trump while they were in town for the NATO summit.  

And an article by US publication Politicoquoted several diplomats and NATO summit attendees who voiced concern about Biden's health. They also voiced frustration over the fact that the ongoing discussion about the US president was taking away from what was supposed to be a celebratory summit for alliance members. Notably, however, the majority of them were quoted anonymously.

Biden's NATO summit opening speech 'strongly delivered'

With everything going on, Biden's opening speech on Tuesday was closely watched and reactions were mostly positive. Politico called it "forceful," while the BBC referred to the speech as "brief but strongly delivered remarks."

Clüver Ashbrook also said the president looked well at the summit's opening in the Mellon Auditorium, where the North Atlantic Treaty was signed in 1949.

"Biden has always proved to be strong on the international stage," Clüver Ashbrook told DW. "He seemed to have regained some of his vigor. Of course, he was reading from a teleprompter but he still managed to stress his key points strongly."

Biden and Trump: two very different positions on NATO

Perhaps Biden was energized by the fact that he could announce NATO plans to send more air-defense systems to Ukraine. The US president has been a strong supporter of Ukraine, pushing for aid packages when Congress was hemming and hawing. He is also a firm believer in the importance of NATO and the US's membership in it.

"An overwhelming majority of Americans understand that NATO makes us all safer," he said, calling support for the alliance a "sacred obligation."

Trump, on the other hand, has said in the past that under his leadership the US would not protect NATO allies from Russian attacks if they hadn't spent the requisite 2% of their GDP on defense.

While he has walked that statement back a little, it's unclear what another Trump presidency would mean for the US's NATO allies.

"One thing is clear from the time that President Trump was in office, and that is you cannot calculate what he does," Heusgen said. "What we need to do is to concentrate on us."

Edited by: Jon Shelton