NATO allies announced Wednesday they had started the long-promised transfer of F-16 jets to Ukraine as leaders meet for a summit in Washington clouded by political uncertainties in the United States.

With the pomp of the three-day gathering in the US capital, President Joe Biden is aiming to rally the West and also reassure US voters amid intense pre-election scrutiny on whether at 81 — six years older than the alliance — he remains fit for the job.

Kicking off events for the 32-nation alliance with a celebration Tuesday evening, Biden committed a new air defense system for Kyiv and urged unity against Russian President Vladimir Putin, who launched the Ukraine invasion in 2022.

“Make no mistake. Ukraine can — and will — stop Putin,” Biden said in a forceful speech.

The White House followed up Wednesday by saying that Denmark and the Netherlands had begun sending F-16 jets to Ukraine.

Biden last year approved the key request by Ukraine, which wants advanced Western aircraft as it struggles to gain parity in the skies with Russia.

Secretary of State Antony Blinken said the F-16 transfer “concentrates Vladimir Putin’s mind on the fact that he will not outlast Ukraine, he will not outlast us and, if he persists, the damage that will continue to be done to Russia and its interests will only deepen.”

“The quickest way to get to peace is through a strong Ukraine,” Blinken said.

But Donald Trump, who is edging out Biden in recent polls, has mused about bringing a quick peace settlement by forcing Ukraine to surrender territory to Russia.

The Republican mogul has repeatedly questioned the utility of NATO — formed in 1949 as collective defense against Moscow — which he sees as an unfair burden on the United States.

On the eve of the summit, Russia fired a barrage of missiles on Ukraine, killing dozens, including in Kyiv where a children’s hospital was reduced to debris.

Biden invited to the summit Ukrainian President Volodymyr Zelensky, who voiced gratitude for the F-16s which he said would better protect his country from such “brutal Russian attacks.”

The new aircraft will “bring just and lasting peace closer, demonstrating that terror must fail everywhere and at any time,” Zelensky wrote on social media.

The summit will look for ways to “Trump-proof” the alliance including by having NATO itself take over coordination of arms delivery from the United States.

Outgoing NATO chief Jens Stoltenberg has also sought a pledge to keep supplying arms at the same rate — some 40 billion euros ($43 billion) annually — that NATO members have been since Russia invaded.

“I expect that regardless of the outcome of the US elections, the US will remain a strong and staunch NATO ally,” Stoltenberg said as leaders gathered for the summit.

Biden has also invited four key Pacific partners — Japan, South Korea, Australia and New Zealand — as he seeks to increase NATO’s role in managing a rising China.

Ukraine wants firm assurances that it will one day join NATO, which considers an attack on any member an attack on all.

A NATO diplomat said negotiations had settled on wording of a statement that will voice support for Ukraine’s “irreversible path to full Euro-Atlantic integration, including NATO membership.”

Kyiv’s membership enjoys wide backing from Baltic and Eastern European nations still haunted by decades under the Soviet yoke.

But Biden and German Chancellor Olaf Scholz have led opposition, concerned that the alliance would effectively be entering war with nuclear-armed Russia as it occupies swathes of Ukraine.

Zelensky, who has achieved hero status in much of the West for his media-savvy defiance of Russia, voiced open annoyance at the last NATO summit in Lithuania at the failure to provide a clearer path to membership.

Other leaders attending the summit include Hungarian Prime Minister Viktor Orban, one of Putin’s closest partners in the West, who ahead of Washington went to Ukraine, Russia and China on a self-described peace mission criticized by Brussels and Washington.

Biden, Blinken and Defense Secretary Lloyd Austin will later welcome their counterparts for gala dinners around the Washington area, which is in the throes of a searing heat wave.

One new NATO leader is British Prime Minister Keir Starmer, who is visiting days after taking office in a landslide victory by his Labour Party.

He will meet both Biden and Zelensky and is expected to confirm Britain’s strong support for Ukraine.