DUBLIN — What began as a triumphant European stopover for President Volodymyr Zelensky of Ukraine has spiraled into a fresh diplomatic clash with Donald J. Trump, after reports of a suspected assassination attempt in Ireland collided with a series of moves from Washington that Kyiv and many European officials view as a reward to Moscow.

Mr. Zelensky received a prolonged standing ovation in the Irish Parliament following a speech that cast the war in Ukraine as a test of whether a “community of nations” can still defend justice against naked aggression. Hours earlier, according to accounts cited by Irish and European officials, four large military-style drones entered the no-fly zone above Dublin International Airport shortly after Mr. Zelensky’s plane landed.

The drones, which reportedly circled the airport before moving east to loiter above a covertly deployed Irish naval vessel in the Irish Sea, were described by officials as an act of “hybrid warfare” and a likely assassination attempt on the Ukrainian leader. Irish authorities and European security services have not publicly named a culprit, but officials quoted in those reports said Russia was “almost certainly” responsible.

Against that backdrop, the Trump administration’s latest sanctions decision landed in Europe with a thud. On the same day as the alleged plot, the U.S. Treasury quietly moved to suspend parts of earlier sanctions on Lukoil, the Russian energy conglomerate, extending a waiver that allows Lukoil-branded gas stations across Europe, Central Asia, the Middle East and the Americas to continue operating outside Russia until at least April 29, 2026.

To Mr. Zelensky’s allies, the timing was impossible to ignore. While European intelligence services were investigating the drone incident and Russia’s broader threats against the continent, Washington was loosening the grip on a flagship Russian energy company. Ukrainian and European officials saw confirmation of a pattern they say has been growing clearer for months: a White House more interested in preserving economic space for Moscow and its partners than in tightening the screws over alleged war crimes and territorial aggression.

In a written statement after the Dublin visit, Mr. Zelensky signaled an increasingly wary tone toward Mr. Trump, even as he pledged to continue formal contacts with the American side. He said Ukrainian representatives would “continue their discussions in the United States with President Trump’s team,” but stressed that Kyiv’s immediate task was to obtain “full information about what was said in Moscow between Witkoff, Kushner and the Russian representatives” — a reference to back-channel talks that European intelligence services are believed to have monitored.

“Ukraine is prepared for any possible developments,” Mr. Zelensky said, underscoring that only a “dignified peace” — not a dictated surrender — could provide real security. Such a settlement, he added, would “continue to require the support of our partners.”

His speech in Dublin made that appeal explicit. “One strong country can start a war,” Mr. Zelensky told Irish lawmakers. “Another strong country can help to stop the war. But to restore justice and defend what’s right, we need a community — a world made up of many different nations.” No power, he said, “not even Russia, not even Putin,” can break that united front if it chooses to stand together.

In Moscow, President Vladimir V. Putin offered a starkly different message. In remarks broadcast on Russian state media, he insisted that Russia did not seek war with Europe, but coupled that reassurance with an unmistakable threat. “If Europe suddenly wants to fight us and starts, we’re ready now,” he said, warning that a larger conflict could leave Russia with “no one left to negotiate with.” He accused Western governments of altering peace proposals in ways “absolutely unacceptable for Russia” in order to blame Moscow for any breakdown in talks.

Former American and NATO officials said the statement fit a longstanding pattern. Russia, they noted, has spent years probing NATO’s defenses and political cohesion through drones entering Polish airspace, fighter jets skimming the skies above Estonia and other acts of sabotage and intimidation. The goal, they argued, is to chip away at confidence in NATO’s mutual defense commitments and sow uncertainty across the continent.

If Mr. Putin’s words were heard as a warning shot, some of the loudest echoes came not from Kyiv but from Europe’s financial capitals. According to recent discussions described by European officials in the video commentary where the Irish events were first highlighted, some EU policymakers are exploring the possibility of dumping as much as $2.43 trillion in U.S. debt should Mr. Trump formally abandon Ukraine and align American policy more closely with the Kremlin’s preferences — a step economists say could trigger financial turmoil exceeding the 2008 crisis.

Mr. Trump, appearing in the Oval Office in footage that critics said showed him visibly fatigued, struck an almost detached tone when asked about the war and a recent visit to Moscow by Jared Kushner and real estate investor Steve Witkoff. He said their “impression” was that Mr. Putin “would like to see the war ended” and return to trade with the United States, but described earlier periods as times when Ukraine “had no cards,” suggesting he believed Kyiv had missed a chance to settle on less favorable terms.

Meanwhile, on Capitol Hill, lawmakers from both parties continued to press for a harder line against Moscow. At a Senate hearing on Russia’s mass deportation of Ukrainian children, Senator Richard Blumenthal of Connecticut called the practice “literally genocide,” aimed at erasing Ukrainian identity. He urged designating Russia a state sponsor of terrorism and using seized Russian assets to support Ukraine’s reconstruction.

The diplomatic theater extended even to the symbolic realm. As Mr. Blumenthal spoke, Russia’s envoy in Washington publicly thanked Melania Trump for her “humanitarian work,” in a statement that Ukrainian officials saw as part of a broader effort to soften the Kremlin’s image in American conservative circles even as rockets and drones continue to strike Ukrainian cities.

For now, Mr. Zelensky’s government is trying to walk a narrowing path: maintaining working contacts with a U.S. administration it increasingly distrusts, shoring up support in European capitals that fear both Russian aggression and American retreat, and reminding a war-weary world that, as he told lawmakers in Dublin, “no one can lie to the entire world forever — not even Putin.”