Just hours before President Volodymyr Zelensky of Ukraine sat down with President Trump in the Oval Office on Friday, Senator Lindsey Graham of South Carolina dispensed some advice to the Ukrainian leader.

“Don’t take the bait,” he said, encouraging him not to get into a spat with Mr. Trump.

“I said, don’t get into arguments about security agreements,” Mr. Graham recalled on Friday evening in a brief telephone interview with The New York Times, as he sat aboard Air Force One preparing to fly to Florida with the president.

Mr. Zelensky did not silence his concerns during his meeting with Mr. Trump, who has come to expect a level of capitulation from almost everyone who has met with him since Election Day, from foreign leaders to billionaire business executives. The result was an extraordinary dressing down by a U.S. president of a foreign ally in the middle of the Oval Office, while the media’s cameras recorded it all.

The question hovering over Washington on Friday evening was whether the confrontation was a spontaneous outburst or a planned verbal smack down by Mr. Trump and Vice President JD Vance, neither of whom respect Mr. Zelensky.

But three people with knowledge of what took place beforehand said neither Mr. Trump nor Mr. Vance had been looking to blow up a deal for Ukraine’s mineral rights, which Mr. Zelensky had been expected to sign in Washington. Instead, they said, Mr. Zelensky seemingly triggered the two American leaders by not sufficiently thanking the United States for trying to end the war (which Mr. Trump wanted to hear) and by pressing for commitments to protect Ukraine from Russian aggression going forward (which Mr. Trump did not want to hear).

In the end, Mr. Zelensky left the White House without a signed deal over mineral rights, which Mr. Trump had sought for weeks, and, for now, an even more contentious relationship with his country’s most important ally.

The day was not supposed to unfold this way.

‘Oh look, you’re all dressed up’

The day before the Oval Office meeting, Mr. Trump called Mr. Graham and invited him to sit in the front row of the White House ceremony when the leaders signed the minerals deal. The president appeared to be on a high, excited about the deal to obtain revenue from Ukraine’s natural resources, Mr. Graham said. Mr. Trump believed it would be a fitting coda to his third foreign leader visit of the week and weeks of negotiations.

Those talks had gone in fits and starts, with a sense of distrust hanging over it all. The Ukrainians felt affronted by the initial proposal; a U.S. team privately accused the Ukrainians of gumming up the discussions. And the Americans separately had peace discussions with Russian officials, which had infuriated the Ukrainians.

Mr. Trump’s two other bilateral meetings this week — with President Emmanuel Macron of France on Monday and Prime Minister Keir Starmer of Britain on Thursday — were chummy affairs, in part because the leaders came prepared to flatter even as they voiced some disagreements with Mr. Trump over his approach to Ukraine.

On Friday morning, Mr. Graham, along with roughly a dozen of his Senate colleagues, met Mr. Zelensky at 9:30 a.m. at the Hay-Adams hotel. During that meeting, Mr. Graham, a close ally of Mr. Trump, shared his advice with Mr. Zelensky on how he should conduct himself at the White House.

Mr. Graham has been one of the most vocal supporters of Ukraine in the Republican Party. Yet his warning to Mr. Zelensky underscored how significantly the G.O.P., business leaders and even some Democrats had reoriented themselves around Mr. Trump’s desires in the wake of his November win.

Senator Richard Blumenthal, a Democrat from Connecticut who also attended the Hay-Adams meeting, said it was “very positive and productive.” When Mr. Zelensky arrived at the White House soon after, Mr. Trump greeted him at the entrance to the West Wing and made a crack about his casual outfit.

“Oh look, you’re all dressed up,” Mr. Trump said, an early signal that he was going into the meeting somewhat peeved. Mr. Zelensky, who says he does not wear a suit to show solidarity with his soldiers, had on the unadorned, military-style clothing he usually wears at official events.

Mr. Trump, Mr. Vance and their advisers have long disliked Mr. Zelensky, complaining that he just wants the United States to provide more money and resources for a war that has no end in sight. Mr. Trump in recent days has tried to shield Vladimir V. Putin, the Russian president, from criticism for instigating the conflict.

But as the two leaders sat down for a bilateral meeting without any cameras, the exchange was cordial, according to one person with direct knowledge of the events.

Then the reporters showed up, and the energy in the room instantly shifted, the person said. About eight minutes into the meeting, journalists started peppering the leaders with questions, exposing the divisions between Mr. Trump and Mr. Zelensky.

Mr. Trump began to grow frustrated at reporters who pressed him on security guarantees, which Ukraine was hoping to get in exchange for giving the United States a share in the country’s mineral wealth.

Those guarantees from Washington, the only nuclear-armed power truly capable of standing up to Russia, had been Mr. Zelensky’s most important demand.

There were several moments of pique, like when, nearly 40 minutes into the meeting, Mr. Trump was asked to address concerns that he was too closely aligned with Mr. Putin. Mr. Trump disputed that, arguing he was prioritizing a peace deal.

At another point, Mr. Trump tried to correct Mr. Zelensky on the year when Russia annexed Crimea, but he provided the incorrect year. Mr. Zelensky then corrected him and reminded the leaders that Mr. Putin had repeatedly broken negotiated cease-fires. Mr. Vance lashed out, telling Mr. Zelensky he was being disrespectful to the president.

But perhaps the most contentious point came when Mr. Zelensky said the war in Ukraine also threatened the United States.

“You have nice ocean and don’t feel now, but you will feel it in the future,” he said.

That prompted Mr. Trump to pile on, telling Mr. Zelensky that he was “not in a very good position” and was “gambling with World War III.” Mr. Trump then mocked a reporter who asked what would happen if Russia broke a cease-fire.

“What if anything?” he asked. “What if a bomb drops on your head right now? OK? What if they broke it? I don’t know, they broke it with Biden because Biden, they didn’t respect him. They didn’t respect Obama. They respect me.”

As the extraordinary argument continued, Oksana Markarova, Ukraine’s ambassador to the United States who was sitting beside the leaders, put her face in her hands.

Finally, Mr. Trump declared that there had been enough, adding that it would make for “great television” before leaving the room.

‘I’m not sure that we did something bad’

Once the meeting ended, Mr. Zelensky and his aides returned to the Roosevelt Room while Mr. Trump huddled with his aides in the Oval Office. The two leaders were supposed to participate in the signing ceremony that Mr. Graham was eager to attend, and then to hold a joint news conference. The delegations were also supposed to have lunch together.

Mr. Trump was still unhappy, and did not want to continue working with Mr. Zelensky that day. Secretary of State Marco Rubio and Michael Waltz, Trump’s national security adviser, were dispatched to the Roosevelt Room to say the rest of the day’s events would be canceled.

One member of the Ukrainian delegation suggested that Mr. Trump and Mr. Zelensky try a one-on-one meeting to reduce the simmering anger; the U.S. officials had no interest.

The president went ahead with the lunch prepared in honor of Mr. Zelensky. He filled the empty seats with some of his top aides, who dined on an early spring green salad, rosemary roasted chicken and crème brûlée. Mr. Trump’s deputy White House chief of staff, Dan Scavino, gleefully posted on social media about the menu.

For years, the Republican Party has fractured over its posture toward Russia. And privately, some operatives said they were aghast at Mr. Trump’s behavior, even as they criticized Mr. Zelensky for what they saw as needless aggravation.

But instead of a massive schism among Republican elected officials after the blowup in the Oval Office, nearly all of them quickly fell in line behind Mr. Trump.

Mr. Graham told reporters outside the White House that Mr. Zelensky should “resign and send somebody over that we can do business with, or change.” Senator Roger Wicker of Mississippi, who told Mr. Zelensky at the Hay-Adams earlier in the day that the senators were there “as a show of support,” took down a post showing him shaking hands with the Ukrainian leader.

A few hours later, Mr. Zelensky appeared on Fox News for a previously scheduled interview, and some Republicans wanted him to apologize for the confrontation at the White House. Instead, Mr. Zelensky expressed some regret about the contentious exchange, but he said he believed he could repair his relationship with Mr. Trump.

“I think that we have to be very open and very honest,” he said. “And I’m not sure that we did something bad.”

As if taking a victory lap, Mr. Trump departed Washington with some of the boxes the F.B.I. had seized from Mar-a-Lago in 2022 as part of the Justice Department’s investigation into his handling of classified documents.

“Justice finally won out,” Mr. Trump said in a statement. “I did absolutely nothing wrong.”

On the flight to Florida, Mr. Trump had the television turned to Fox News, watching Mr. Zelensky’s interview.