In a fiery public confrontation unlike any seen between an American president and foreign leader in modern times, Mr. Trump and Mr. Vance castigated Mr. Zelensky for not being grateful enough for U.S. support in Ukraine’s war with Russia, and sought to strong-arm him into making a peace deal on whatever terms the Americans dictated.

With his voice raised and temper flaring, Mr. Trump threatened to abandon Ukraine altogether if Mr. Zelensky did not go along. After journalists left the Oval Office, Mr. Trump canceled the rest of the visit, including a planned joint news conference and signing ceremony for a deal on rare minerals, and U.S. officials told the Ukrainians to leave. A grim-faced Mr. Zelensky strode out, climbed into a waiting black sport utility vehicle and departed the White House grounds.

“I have determined that President Zelenskyy is not ready for Peace if America is involved, because he feels our involvement gives him a big advantage in negotiations,” Mr. Trump wrote on social media. “I don’t want advantage, I want PEACE. He disrespected the United States of America in its cherished Oval Office. He can come back when he is ready for Peace.”

“The president’s verbal assault on Mr. Zelensky was a stunning display of anger and resentment toward the leader of a country that has been invaded by a larger power intent on eliminating it as an independent state. No other president in memory has lashed out at a visiting foreign leader in the Oval Office on camera in such a vituperative way, not even at an adversary of the United States, much less a putative ally.”

“The spectacle underlined how radically Mr. Trump has reoriented American foreign policy in less than six weeks back in office, all but switching sides in the war in Europe as he expresses sympathy for President Vladimir V. Putin of Russia and antipathy for Mr. Zelensky.

Even as he shouted at the Ukrainian leader in the Oval Office, the president spoke of Mr. Putin as if they were friends, saying that the Russian leader has “been through a lot with me” in enduring the “Russia hoax,” referring to the investigation of Mr. Putin’s clandestine efforts to help Mr. Trump win the 2016 election.”

“America’s traditional European allies, on the other hand, were deeply alarmed and rallied behind Mr. Zelensky, with the leaders of France, Germany, Poland and others issuing statements of support for Ukraine and its beleaguered leader. The show of solidarity came just days after the United States sided with Russia over Europe in opposing a U.N. resolution condemning Russian aggression on the third anniversary of its full-fledged invasion of Ukraine.”

“Mr. Vance’s eagerness to assail Mr. Zelensky raised the question of whether it was a planned or impromptu ambush. Mr. Vance has never been a supporter of Ukraine and said in 2022 that “I don’t really care what happens to Ukraine.””

After Mr. Vance began chastising Mr. Zelensky, it seemed to prompt Mr. Trump to join in. The result, though, was the blowup of an economic deal that Mr. Trump had prioritized in recent days, a commitment by Ukraine to turn over rare mineral rights to repay U.S. military aid over the past three years. The future of that deal remained unclear. A Trump administration official said later on Friday that all U.S. aid to Ukraine could be canceled imminently.

“It was a measure of how much Republicans have fallen behind Mr. Trump that Mr. Graham and Secretary of State Marco Rubio, both onetime hawks and strong supporters of Ukraine against Russia, backed the president and vice president.”

“Mr. Zelensky tried to respond to Mr. Vance’s assertions and said that the United States could feel threatened by Russia some day. “You have a nice ocean and don’t feel now, but you will feel it in the future,” he said.

That set off Mr. Trump, who cut off Mr. Zelensky. “Don’t tell us what we’re going to feel,” he said, raising his voice. “You’re not in a good position. You don’t have the cards right now.”

“I’m not playing cards,” Mr. Zelensky replied. “I’m very serious, Mr. President. I’m the president in a war.””

“We stand with Ukraine in good and in testing times,” wrote Friedrich Merz, set to be Germany’s next chancellor after elections this week. “We must never confuse aggressor and victim in this terrible war.”

“A few moments later, Mr. Zelensky again cited Mr. Putin’s role in the war and suggested that Mr. Trump was listening to the Russian leader too much. In response to Mr. Trump’s comment that Ukrainian cities were destroyed, Mr. Zelensky said no, they had survived despite Russian bombardment.

“Maybe it’s Putin who’s sharing this disinformation that he destroyed us,” Mr. Zelensky said.

Mr. Trump came to Mr. Putin’s defense. “He had to suffer through the Russia hoax,” he said, referring to the investigation during his first term into Russian interference on Mr. Trump’s behalf during the 2016 election. “I think that he wants to make a deal and he’d like to see an end.”

“In fact, the investigation by the special counsel Robert S. Mueller III was no hoax and concluded definitively that Mr. Putin ordered an intelligence operation to tilt the election eight years ago to Mr. Trump. Although Mr. Mueller said in his final report in 2019 that “the evidence was not sufficient to support criminal charges,” he made clear that Mr. Trump’s campaign benefited from Russian assistance.”

“But what was particularly striking in their exchange was how much Mr. Trump seemed insulted on Mr. Putin’s behalf. He has long been an open admirer of Mr. Putin and has rarely offered any criticism of his own. Just this week, he called Mr. Putin “smart” and “cunning,” and declined to call him a dictator even after calling Mr. Zelensky that.

“You want me to say really terrible things about Putin and then say, ‘Hi, Vladimir, how are we doing on the deal?’” Mr. Trump told Mr. Zelensky on Friday. “It doesn’t work that way.””

“He did not explain why it was OK to say terrible things to Mr. Zelensky while pursuing a deal. Instead, he portrayed the Ukrainian leader as unreasonably distrustful of Mr. Putin, who has broken multiple agreements guaranteeing Ukrainian sovereignty and calling for cease-fires and now faces an international arrest warrant for war crimes.

“You see the hatred he’s got for Putin,” Mr. Trump said with a tone of indignation as cameras recorded the exchange. “It’s very tough for me to make a deal with that kind of hate. He’s got tremendous hatred. And I understand that. But I can tell you the other side’s not exactly in love with him either.”

He came back to Mr. Putin and the Russia investigation again near the end of the session, describing the Russian leader as if they had bonded through a shared ordeal. “Putin went through a hell of a lot with me,” Mr. Trump said. “He went through a phony witch hunt where they used him and Russia, Russia, Russia, Russia.”

The affront to Mr. Putin seemed to stick with Mr. Trump. By evening, hours after tossing Mr. Zelensky out of the White House, Mr. Trump stopped to talk with reporters as he left for a weekend in Florida and again outlined his grievance with the Ukrainian president.

“He’s got to say, ‘I want to make peace,’” Mr. Trump said. “He doesn’t have to stand there and say about, ‘Putin this, Putin that,’ all negative things. He’s got to say, ‘I want to make peace.’””