President Biden said it’s important for Ukraine’s Western allies to “sustain our resolve” in supporting the country as he held meetings Friday with European partners, with the upcoming U.S. presidential election casting a long shadow over his visit to Germany.

Mr. Biden met with Chancellor Olaf Scholz of Germany, Ukraine’s second-biggest military supplier after the U.S. They were joined by French President Emmanuel Macron and British Prime Minister Keir Starmer for discussions that were also addressing the conflict in the Middle East.

With the election just weeks away and the race extremely tight, there are worries that a victory for Donald Trump, the Republican nominee, could upset the relationships that Mr. Biden is hoping to pass on to Vice President Kamala Harris, the Democratic nominee.

Trump has an appetite for imposing trade tariffs on key U.S. security partners. He has expressed indifference to the security of Ukraine, refusing to say during a presidential debate if he wants the U.S. ally to win its war against Russia. He’s voiced doubts about coming to the defense of NATO members if they come under attack.

The gathered leaders never uttered Trump’s name in public, yet their remarks often hinted at the possibility that he could withdraw support from Ukraine and scorn global alliances that Mr. Biden and his counterparts view as critical.

“As Ukraine faces a tough winter, we must — we must — sustain our resolve, our effort and our support,” Mr. Biden said. “And I know the cost is heavy. Make no mistake, it pales in comparison to the cost of living in the world where aggression prevails, where large states attack and bully smaller ones simply because they can.”

Scholz said that “we will stand beside Ukraine as long as it is necessary,” pointing to a planned $50 billion international loan package funded by interest on profits from frozen Russian assets.

“Our position is clear: We are supporting Ukraine as strongly as possible,” he added. “At the same time, we are taking care that NATO does not become a party to the war so that this war doesn’t culminate in an even bigger catastrophe.”

Scholz has indicated that he’s skeptical about aspects of a “victory plan” drawn up by Ukrainian President Volodymyr Zelenskyy, and says he will stand by his refusal to supply Taurus long-range cruise missiles to Kyiv.

Mr. Biden didn’t want his term to end without visiting Berlin, after having been to other key allies such as Japan, South Korea, France, India, the U.K., Poland and Ukraine.

Concerns about what might come next were reflected as Mr. Biden received the highest class of Germany’s Order of Merit, which was also bestowed on former U.S. President George H.W. Bush in recognition of his support for German reunification.

German President Frank-Walter Steinmeier said the friendship with the U.S. is “and will always be existentially important” for Germany, but there have always been “times of proximity and greater distance.”

“Even recently, just a handful of years ago, the distance had grown so wide that we almost lost each other,” Steinmeier said, in an reference to tense relations during Trump’s earlier presidency. He said Mr. Biden “restored Europe’s hope in the trans-Atlantic alliance literally overnight.”

“In the months to come, I hope that Europeans remember: America is indispensable for us,” he added. “And I hope that Americans remember: Your allies are indispensable for you. We are more than just ‘other countries’ in the world — we are partners, we are friends.”

Recalling the “wide sweep of history” he has seen in his 81 years, Mr. Biden said, “we should never underestimate the power of democracy, never underestimate the value of alliances.”

As he met Scholz, Mr. Biden said he was “grateful for Germany’s cooperation in holding Iran accountable for destabilizing policies, including providing missiles and drones to Russia to use against Ukraine.” He pointed to new European sanctions against Iran’s leading airlines and said that “this coordination is going to have to continue.”

Mr. Biden reiterated his call for Israel to pursue peace after the killing of Hamas leader Yahya Sinwar — which he described as “a moment of justice.”

“I told the prime minister of Israel yesterday, let’s also make this moment an opportunity to seek a path to peace, a better future in Gaza without Hamas,” he said.

Trump has said his approach will help the U.S. economy and prevent foreign countries from taking advantage of the United States. He maintains that if he were still president, Russia would never have invaded Ukraine in 2022 and Hamas would never have attacked Israel in 2023.

“I will end the war in Ukraine, stop the chaos in the Middle East, and prevent World War III,” he said at a recent rally in Georgia.

Harris, for her part, has voiced strong backing for Ukraine and tracks with Mr. Biden on support for Israel, while placing particular emphasis on the need to relieve the suffering of Palestinian civilians whose lives have been upended by the Hamas-Israel war.