KYIV, Ukraine—A half-year ago in the Oval Office, President Trump told Ukrainian President Volodymyr Zelensky that “you don’t have the cards” in the war with Russia. On Tuesday at the United Nations, Trump lauded the performance of Ukraine’s army and poured scorn on Russia’s military efforts.

“I think Ukraine, with the support of the European Union, is in a position to fight and WIN all of Ukraine back in its original form,” Trump said on Truth Social after meeting with Zelensky. “Why not?”
The sharp verbal shift from Trump came amid Russia’s continued failure to make significant gains on the battlefield, a slowdown in the Russian economy and a concerted effort by Zelensky to woo the U.S. president.
Zelensky showed on Tuesday that he has learned from the disastrous meeting with Trump in February. He has smartened up his attire after criticism from Trump supporters and, seated next to the U.S. president ahead of the Tuesday meeting, repeatedly thanked him for his support, praising his efforts to end the war while talking up the performance of the Ukrainian army on the battlefield.
Trump, Zelensky said later, “clearly understands the situation and is well-informed about all aspects of this war.”
It is far from certain that Trump’s shift in tone will be reflected in a change in policy. He has so far proved unwilling to impose significant sanctions on Russia, despite making threats to do so, or provide the kind of surge of weapons that Ukraine would need to retake significant territory and protect its cities from Russian aerial bombardments.
Kremlin spokesman Dmitry Peskov said Wednesday that Zelensky’s view was currently dominant with Trump, but that Russia would have opportunities to convey its position to the White House.
In Ukraine, some welcomed Trump’s comments with cautious optimism. Andriy Yermak, the chief of staff to Zelensky, posted an emoji of a bicep alongside a screenshot of a White House social-media post calling the Ukrainian president “a brave man.” But opposition lawmaker Yaroslav Zheleznyak said on social media that Trump’s words don’t mean anything and wouldn’t have any consequences.
Still, the U.S. president’s apparent reappraisal of Ukraine’s chances in the war also came with a commitment to continue providing weapons to European members of the North Atlantic Treaty Organization, which then pass them on to Ukraine to use against Russia.
Zelensky’s rehabilitation is all the more surprising given the mauling he took in the Oval Office in February. That meeting was supposed to clear the air after Zelensky said he was worried that the U.S. president was adopting Kremlin talking points. Trump fired back that Zelensky was a “dictator without elections.”
But the meeting descended into acrimony when Vice President JD Vance accused Zelensky of being ungrateful for American help. After Zelensky sought to defend himself against Trump and Vance, Trump’s team evicted the Ukrainian delegation from the White House.
Zelensky sought to patch up relations by expressing regret in a letter and quickly agreeing to a U.S. proposal for a cease-fire while Russia demurred. As Trump pushed for a quick peace deal, Zelensky trod a fine line between backing the U.S. president’s aims while pushing back on ideas that would be unacceptable to Ukrainians, such as formally ceding territory to Russia.
A meeting at the funeral of Pope Francis appeared to heal the rift and boost Zelensky’s standing. The two men met privately for 15 minutes in St. Peter’s Basilica in what Trump later called “a beautiful meeting.” Afterward, Trump offered rare criticism of Russian President Vladimir Putin.
Zelensky has shown that he has learned from the meeting with Trump in February.
When Zelensky returned to the White House in August, he wore a black suit-style jacket after his military-style attire at the February meeting sparked a testy exchange with a pro-Trump reporter. Trump praised his look and the meeting was more cordial, with the U.S. leader proposing a peace conference with Putin.
By Tuesday, Trump had adopted some of Zelensky’s talking points. He mocked Russia’s army for its slow progress against a much smaller nation and praised Ukrainian troops. “We have great respect for the fight that Ukraine is putting up,” he said. “It’s pretty amazing, actually.”
Trump also slated Russia’s economy, saying it “is terrible right now,” and when Zelensky praised Trump’s initiative to press European allies to stop buying Russian oil, he indicated he would lean on Hungarian Prime Minister Viktor Orban, referring to him as a friend.
Trump said that while he hadn’t spoken with Orban yet, he felt the Hungarian leader would change his mind if he did.
“And I think I’ll be doing that,” Trump added.
Write to James Marson at james.marson@wsj.com
