Following a five-week period where President Trump made it clear that he intends to discard America’s traditional power sources—its alliances with like-minded democracies—and return to an era of raw negotiations among great powers, one crucial question remained unanswered: How far would he go in sacrificing Ukraine for his vision?

The shocking verbal exchange that unfolded in the Oval Office on Friday, witnessed by cameras, provided the response.

As Mr. Trump rebuked President Volodymyr Zelensky and warned him that “you don’t have the cards” to negotiate with President Vladimir V. Putin of Russia, and as Vice President JD Vance berated the Ukrainian leader as being “disrespectful” and ungrateful, it was clear that the three-year wartime partnership between Washington and Kyiv had been broken.

Whether this relationship can be mended, and whether the deal to provide the United States revenue from Ukrainian minerals— the ostensible reason for Zelensky’s visit—can be salvaged, remains uncertain.

However, the more significant reality is that the venomous exchange—broadcast not only to an astounded audience of Americans and Europeans who had never witnessed such open attacks on each other but also to Mr. Putin and his Kremlin aides—made clear that Mr. Trump views Ukraine as a barrier to what he sees as a more vital project.

According to a senior European official, what Mr. Trump truly desires is a normalization of relations with Russia. If rewriting the history of Moscow’s illicit invasion three years ago, halting investigations of Russian war crimes, or refusing to offer Ukraine lasting security guarantees is what it takes to achieve this, then Mr. Trump, based on the assessment of his intentions, is willing to make that deal.

Listening closely, this goal was just beneath the surface when Mr. Zelensky visited Washington for his ill-fated visit.

Secretary of State Marco Rubio—once a staunch defender of Ukraine and its territorial sovereignty, now swayed by Trump’s power plays—made it clear in an interview with Breitbart News that it was time to move on from the war, aiming to establish a triangular relationship among the United States, Russia, and China.

“We’re going to have disagreements with the Russians,” Mr. Rubio said, carefully avoiding language that might accuse Russia as the aggressor, implying that there is a risk that if not punished for its attack on Ukraine, Russia might target a NATO nation next.

“These are powerful nations with nuclear stockpiles,” he said of Russia and China. “They can exert power globally. I believe we have lost the concept of maturity and sanity in diplomatic relations.”

Mr. Trump makes no secret of his belief that the post-World War II system, established by Washington, has diminished American power.

Above all, this system valued relationships with allies committed to democratic capitalism, maintaining those connections even when it cost American consumers. It aimed to prevent power grabs by making the observance of international law and respect for established international boundaries a primary goal.

To Mr. Trump, such a system has granted smaller and weaker countries leverage over the United States, leaving Americans to bear an unfair burden in defending allies and promoting their prosperity.

While his predecessors—both Democrats and Republicans—insisted that alliances in Europe and Asia were America’s greatest force multipliers, maintaining peace and allowing trade to flourish, Mr. Trump viewed them as a drain. In the 2016 presidential campaign, he repeatedly questioned why America should defend countries with trade surpluses at the expense of its own interests.

In the five weeks since his second inauguration, Mr. Trump has initiated a plan to dismantle that system. This explains his demand for Denmark to cede Greenland to the United States, and for Panama to return the canal that Americans built. When questioned about seizing sovereign territory in Gaza for redevelopment in his plan for a “Middle Eastern Riviera,” he responded, “Under U.S. authority.”

However, Ukraine presents a more complicated scenario. Just 26 months ago, Mr. Zelensky was welcomed in Washington as a champion of democracy, invited to address a joint session of Congress, and applauded by Democrats and Republicans alike for standing firm against the aggressive actions of a ruthless foe.

Mr. Trump and Mr. Vance had hinted for months that in their view, America’s commitment to Ukraine’s sovereignty was over. Three weeks ago, Mr. Trump told an interviewer that Ukraine, a former Soviet republic that embraced independence, forged close ties to Western Europe, and sought NATO membership, “may someday be Russian.”

To the dismay of America’s allies, Mr. Vance traveled to the Munich Security Conference two weeks ago and failed to mention security guarantees for Ukraine in any armistice or cease-fire, or to address Russia’s responsibility for its invasion.

Instead, Mr. Vance appeared to embrace the rising far-right party in Germany and its counterparts across Europe. The language of the Biden era, about standing with Ukraine “as long as it takes” to deter Russia from expanding westward, was gone.

Mr. Zelensky was aware of all this—he was in Munich too—which his European defenders understood. While President Emmanuel Macron of France and Prime Minister Keir Starmer of Britain visited the Oval Office with detailed plans to appease Mr. Trump and explain Europe’s increased military spending, Mr. Zelensky took the bait, especially when Mr. Vance started ridiculing Ukraine’s recruitment efforts.

He turned confrontational, telling Mr. Trump that the oceans between America and Russia would not provide perpetual protection. Mr. Trump raised his voice, suggesting that Ukraine would be fortunate just to secure a cease-fire, implying that any terms or no terms would be preferable to its inevitable defeat.

“I want guarantees,” Mr. Zelensky retorted. Moments later, he left the White House, his lunch of rosemary roasted chicken and crème brûlée uneaten, the minerals agreement unsigned, and Ukraine’s future ability to resist a renewed Russian push to topple Kyiv in doubt.

Various parts of the world quickly retreated to their familiar positions.

Mr. Macron aligned with the Ukrainian leader, urging the West to thank Ukrainians for being freedom’s frontline defense. He was backed by nervous Eastern European countries, led by Poland, Lithuania, and Latvia. Yet, in private, several European diplomats believed the damage could be irreparable.

The Russians celebrated their good fortune. Former President Dmitri A. Medvedev thanked Mr. Trump for “telling the truth” to Mr. Zelensky face-to-face. He urged him to stop the remaining American aid.

Mr. Rubio was among the first to congratulate the president for putting in his place a leader he once compared to a modern-day Churchill in a T-shirt.

“Thank you @POTUS for standing up for America in a way that no President has ever had the courage to do before,” Mr. Rubio wrote on social media. “Thank you for putting America First.”

Of course, echoing Mr. Trump’s favorite slogan and shattering an established global order is easier than creating a new one. Assembling the post-World War II rules of global engagement took decades, and for all its flaws, the system was successful in its primary objectives: preventing great power wars and promoting economic interdependence.

Mr. Trump has yet to articulate in detail what rules he would replace them with, other than utilizing America’s military and economic might to negotiate deals—basically arguing that peacekeeping is as straightforward as weaving together minerals agreements and trade pacts, possibly with a few real estate transactions included.

There is scant precedent to suggest this approach works, particularly with authoritarian leaders like Mr. Putin and President Xi Jinping of China, who adopt a long-term view when dealing with democracies, viewing them as lacking the willpower to achieve challenging goals.

However, judging by the display in the Oval Office on Friday, Mr. Trump appears convinced that as long as he is in control, the world will order itself according to his wishes.