LONDON — The U.S. has been Ukraine’s biggest military backer since Russia’s full-scale invasion began three years ago. The suspension of that aid by the Trump administration doesn’t mean Ukraine’s defenses will quickly collapse.

But it’s a major blow that threatens to remove some of the most formidable weapons in Ukraine’s battlefield arsenal, and ratchets up pressure on Kyiv to accept a peace agreement.

U.S. Aid to Ukraine: A Crucial Lifeline

The United States has given the Ukrainians more than $180 billion in assistance since Russia launched an all-out war on Feb. 24, 2022, including more than $66.5 billion in military aid.

Washington provides about 20% of Ukraine’s military supplies, and that fifth includes the most lethal and important equipment, including longer-range missiles and Patriot air defense systems that can shoot down the most powerful Russian projectiles.

American military assistance also goes far beyond weapons and ammunition.

Ukrainian troops rely on satellite communications systems supplied by Elon Musk’s Starlink to communicate on the front line, and on American intelligence to track Russian troop movements and select targets for Ukrainian strikes. If the U.S. stops sharing data from satellites and other assets, it would badly affect Ukraine’s capability to strike back at Russia, and Ukraine’s other allies lack the resources to fill the gap.

“A lot will depend on what’s covered by the American suspension,” said Malcolm Chalmers, deputy director-general of defense think-tank RUSI. “Will they suspend all technical assistance to Ukraine? That would have a more dramatic, more rapid impact than simply stopping the pipeline of arms.”

Trump’s Decision and Its Implications

The White House said that the U.S. is “pausing and reviewing” its Ukraine aid to “ensure that it is contributing to a solution.” The order will remain in effect until Trump determines that Ukraine has demonstrated a commitment to peace negotiations with Russia.

The decision comes days after an explosive meeting with Ukrainian President Volodymyr Zelenskyy, in which Trump and U.S. Vice President JD Vance said that Ukraine’s leader hasn’t expressed sufficient gratitude for American support.

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Battlefield Impact and Ukraine’s Resilience

The U.S. move won’t have an immediate impact on the battlefield, where Kyiv’s forces are struggling to stem a relentless Russian offensive in eastern Ukraine. Ukrainian forces have slowed Russian advances along the roughly 1,000-kilometer (600-mile) front line, where Russia is slowly gaining ground at a huge human and material cost.

The pause in aid will weaken air defenses and will hit Ukraine’s ability to hit Russian targets far behind the front lines.

Alexander Kots, a Russian war blogger, said that for Ukraine, “the U.S. aid suspension is unpleasant but not deadly.”

He said that while Ukraine’s European allies can fill some of the gaps and provide artillery systems, they don’t have alternatives to the U.S.-made air-defense systems and longer-range HIMARS missile systems that can strike ground targets up to 300 kilometers (200 miles) away.

Ukraine is already running low on missiles for the American-supplied Patriot systems that are crucial to defending cities from Russian air attacks, according to Patrick Bury, a warfare expert at the U.K.’s University of Bath.

“The problem is, a lot of what the U.S. provides is the stuff that Europe cannot, and other countries cannot, provide in the short term – high-end stuff,” he said.

Ukraine has stockpiles of artillery shells and other munitions, and has ramped up domestic production of drones, which are now among the most important weapons in the war. It’s estimated that just over half of the military hardware used by Ukraine is domestically produced.

Chalmers, the RUSI expert, said that the Ukrainians have built up their defense production, and “are innovating at an incredible rate because of the pressure they’re under.”

“I think they will survive for quite some time,” he said. “But it’s a material blow, and it’s also a challenge to Europe.”

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Europe’s Response and Future Outlook

A summit in London on Sunday was aimed at getting European leaders to step up and put Ukraine in the best possible position before potential peace talks.

The U.K. announced that it would use 1.6 billion pounds ($2 billion) in export financing to supply 5,000 air defense missiles. The European Union has proposed an 800 billion-euro ($841 billion) plan to bolster the defenses of EU nations and provide Ukraine with military muscle.

But Samir Puri, director of the Center for Global Governance and Security at international affairs think tank Chatham House, said that European and American aid are intertwined.

“This was always a joint effort,” he said. “The U.S. gives a lot, the Europeans give a lot. You take away the Americans from that joint effort and … there’s just a huge component missing to the structure.”