Can Ukraine Fight Without U.S. Aid? Seven Questions to Ask

The Trump administration has repeatedly threatened to walk away from Ukraine if there is no progress on a peace deal between Ukraine and Russia. Although the administration has sent mixed signals, its threat is not empty. On March 3, 2025, the United States suspended military aid and intelligence sharing to Ukraine following a tense meeting between President Trump and President Zelensky on February 28, only lifting the suspension on March 11.

A U.S. suspension of military support to Ukraine would be a grievous blow to Kyiv. But would it be fatal? Ukraine’s own resolve has been formidable even after three years of war, and Europe, which already provides tens of billions of euros in financial and military aid, might play a still greater role. This paper argues that a complete U.S. military and intelligence aid cutoff would significantly harm Ukraine’s ability to fight Russia but would not necessarily lead to immediate defeat—and that more limited cutoffs would have more limited effects on Ukraine’s battlefield performance. But the exact extent to which a U.S. cutoff would harm Ukraine depends on Europe’s ability to fill the gap with its own capabilities. Ukraine currently relies heavily on U.S. systems, training, intelligence, and logistics, and although European support and Ukraine’s own defense industry are substantial and growing, they cannot fully replace U.S. capabilities—particularly in the areas of air defense and intelligence assistance for precision targeting. The result is that continued U.S. aid remains extremely important for Ukraine’s long-term effectiveness on the battlefield. The broader geopolitical implications of a U.S. withdrawal could embolden Russia and its allies while straining transatlantic unity.

Understanding the true impact of a cutoff, however, requires a deeper understanding of the types of weapons involved, European and Ukrainian capabilities absent the United States, and how China and other Russian allies would respond. The responses to the seven questions below illustrate the impact of a cutoff, important ambiguities regarding several key specifics of the U.S. threat, and the possibilities and limits of non-U.S. sources of aid.
 

1. What Types of Aid Does the United States Provide Ukraine?

Since Russia’s full-scale invasion of Ukraine in February 2022, the United States has committed $66.5 billion in military assistance to bolster Ukraine’s defense as well as over $50 billion in financial aid. Although destined for Ukraine, 90 percent of this military aid consists of money spent in the United States to build new weapons or to replace weapons sent to Ukraine from U.S. stockpiles. Across all U.S. aid to Ukraine, 60 percent is spent in the United States, about 25 percent is spent in Ukraine, and the final 15 percent is spent elsewhere.

U.S. aid has been delivered through multiple channels—primarily Presidential Drawdown Authority (PDA), the Ukraine Security Assistance Initiative (USAI), and Foreign Military Financing (FMF)—enabling both immediate deliveries to the battlefield and longer-term defense capacity building. The United States has also facilitated third-party transfers and commercial sales while coordinating with allies, who have contributed great quantities of additional military systems and munitions.

The United States has also provided extensive training to Ukraine’s armed forces since Russia’s invasion, helping improve everything from small unit tactics and logistics to leadership development and combined arms operations. In addition, U.S. personnel have delivered platform-specific instruction on systems such as M777 howitzers, Patriot air defense batteries, Bradley infantry fighting vehicles, HIMARS rocket launchers, and F-16 fighter jets. These efforts have been conducted through various channels, often in coordination with NATO and via rotational deployments of U.S. Army and National Guard units to training sites in Europe.

In addition to military equipment and training, the United States has provided Ukraine with extensive intelligence support, including signals intelligence (SIGINT), imagery intelligence (IMINT), and human intelligence (HUMINT). This support has enabled Ukraine to counter missile barrages, disrupt covert operations, and track force movements. Notably, U.S. intelligence has played a pivotal role in Ukraine’s targeting processes for precision strikes, particularly for precision-guided systems like HIMARS. Reports indicate that Ukrainian forces rely heavily on U.S.-provided coordinates for the majority of their strikes conducted with advanced weapons systems, underscoring the extent to which the United States has been integrated into Ukraine’s “kill chain”—the process of identifying, tracking, and eliminating targets using a mix of sensors and platforms.

U.S. support for Ukraine also extends beyond battlefield tools and intelligence, encompassing military planning, and long-term capacity building. The United States has worked closely with Ukraine to coordinate its battlefield strategy and objectives, boost its cyber defenses, tackle corruption, sustain its economy, build its defense industrial capacity, and plan for recovery. The United States also manages transportation and logistics for aid to Ukraine.
 

2. How Extensive Would a U.S. Cutoff Be?

Should the Trump administration decide to end aid to Ukraine, much will depend on the specifics of what “end” means in practice. A cutoff could range from an abrupt halt to all assistance, including preventing allies from providing any support involving U.S. systems, to a more limited, but still painful, cutoff of future transfers by the United States. There are a range of scenarios with varying implications for Ukraine’s security.

While the future of U.S. assistance to Ukraine is uncertain, a funding cutoff would not necessarily bring an immediate end to ongoing weapons deliveries. Much of the assistance already approved by Congress is still in the delivery pipeline and will continue arriving in Ukraine for the next several years, barring an administration decision to cancel already-committed support. That means weapons and support from contracts signed in the past three years will continue flowing to Ukraine for years to come, although training on systems could be cut off. Aid delivered through the PDA, which pulls equipment directly from U.S. military stockpiles, typically takes about eight months from announcement to delivery, according to previous CSIS analysis. By contrast, aid delivered through the USAI—which contracts with defense manufacturers to build new systems—has a much longer timeline: about four months to finalize contracts, two years to produce the first equipment, and up to another 20 months to complete delivery. USAI contracts signed early in the war have begun delivering to Ukraine.

In the instance of a cutoff, an important question is whether Europe would be allowed to transfer military equipment and intelligence it receives from the United States to Ukraine. For military equipment, this would occur through Third Party Transfers (TPT). The United States requires any recipient of defense goods or services to obtain written approval from the Department of State before using or disposing of them in ways not covered by the original acquisition agreement. Belgium, Denmark, the Netherlands, and Norway have pledged to give 65 of their F-16 fighter jets to Ukraine, with some transfers already completed. In January 2022, the United States approved TPTs for Estonia, Latvia, and Lithuania to send U.S.-produced missiles to Ukraine in preparation for the expected Russian invasion. NATO members are also allowed to share certain intelligence originating from U.S. sources and methods with Ukraine, but Washington similarly could halt such sharing. It is also unclear whether the United States would continue to transmit to Europe important tactical intelligence such as details about Russian troop movements and logistics that Ukraine uses to target long-range strikes.

In addition to European countries transferring their own U.S.-manufactured equipment in the instance of a cutoff, the United States could allow Europe to purchase additional U.S. arms and equipment and transfer them directly to Ukraine. In February, President Trump stated he was open to such a proposal. For instance, Europe could purchase AMRAAM and Patriot missiles from the United States and then export them to Ukraine. This would benefit U.S. companies and ensure Ukraine maintains access to key weapons systems.

Washington could also encourage, or allow, Starlink to withdraw services from Ukraine. Ukraine’s military depends on Starlink for command and control, and developing an alternative would be time-consuming and difficult. In the short term, the loss of Starlink could greatly hinder Ukrainian military operations, reducing its nimbleness (a key advantage over Russia) and ability to respond rapidly to any potential Russian breakthroughs.

The United States could also stop the maintenance and repair of existing U.S. weapons systems that Ukraine has received or purchased from the United States. Combat involves constant damage to and wear and tear on equipment, and Ukraine has thousands of pieces of military equipment that require repair. The United States could also prevent European allies from purchasing spare parts for Ukraine.

The worst-case scenario for Ukraine is the United States bars all aid—military and intelligence—from use and discontinues arms sales, even via third parties. For now, a full cutoff of U.S. support to Ukraine seems like an unlikely scenario. On April 30, 2025, President Trump approved $50 million of direct commercial sales to Ukraine, according to Ukrainian media. This, along with the new reconstruction investment agreement, indicates a shift away from previous rhetoric on Ukraine. That said, U.S. rhetoric and policy declarations have oscillated, and a full cutoff remains a possibility.
 

3. Could Europe Step Up?

In addition to the genuine commitment many European governments have to Ukraine’s security, a strong and independent Ukraine is one of Europe’s best defenses against future Russian aggression elsewhere in Europe. Europe already provides considerable military aid, and it could provide more if U.S. support wavers or disappears.

In rhetoric, at least, most European countries are strongly behind Ukraine. In a fact sheet released on April 30, 2025, the United Kingdom reported that “We are proud to be a leading partner in providing vital support to Ukraine.” Germany’s new chancellor, Friedrich Merz, stated before assuming office that “it is clear that the Americans, at least this part of the Americans, this administration, are largely indifferent to the fate of Europe” and has expressed his desire for European defense to become “independent” from the United States. During the European Union’s 2025 defense summit, President of the European Council Antonio Costa stated that “We are here to defend Ukraine.”

Indeed, Europe could play an even greater role in Ukraine’s defense, offsetting, albeit incompletely, a U.S. withdrawal of support. Europe could increase bilateral aid to offset the loss of U.S. support. This would require almost doubling European aid from €44 billion to €82 billion.

Although much of the discussion of European defense focuses on the weaknesses of and gaps in Europe’s militaries and defense industrial base, Europe has, as Barry Posen points out, significant combat power, including large numbers of forces, considerable equipment, and a large defense industry. Europe has already provided Ukraine with advanced military systems, such as those in Table 2.

In addition to providing aid, European states have trained more Ukrainian troops than the United States, totaling over 70,000 individuals. Despite their rhetoric, European states have no desire to send troops to Ukraine while combat is raging, and even a peacekeeping force would be unpopular with many publics if it involved significant risk to the deployed soldiers.

Currently, Europe cannot replace U.S. support in several areas. Europe has a large defense industrial base, but it has many problems. Although Europe’s collective economic strength dwarfs that of Russia, Europe is not on a war footing, while Russia is. Expanding production for artillery, ammunition, and other essentials is possible, but such an expansion would be time-consuming. Despite more than three years of war in Ukraine, Europe has made only limited progress. Europe’s defense supply chains are poorly designed, and despite years of effort, many European companies do not work well across national borders, preventing them from achieving economies of scale.

Without purchases from U.S. companies, Europe would have difficulty providing large numbers of munitions, such as 155 mm artillery rounds, given the significant numbers Ukraine expends every day and Europe’s weak defense industrial base. The United States has provided over 3 million 155 mm artillery rounds since the start of the conflict. Europe has stretched its production, increasing from roughly 300,000 a year as of February 2023 to nearly 1 million today. Even with the European Union’s goal of increasing production to 2 million rounds annually, removing U.S. production would leave a large gap in Ukraine’s supplies.

In addition to artillery shells, Ukraine depends on U.S.-supplied systems like HIMARS and ATACMS to strike targets along and far behind the front lines. These long-range precision systems have been critical to hitting high-value Russian targets, including command posts, supply lines, troop concentrations, artillery systems, and ammunition depots. Europe does not field equivalents at comparable scale or capability and could not readily replace them if U.S. support ceased.

Europe could attempt to offset a halt of aid by providing financing for Ukraine to purchase South Korean, Israeli, and other long-range strike systems. However, it remains unclear what capabilities these countries could or would provide, at what scale, how quickly they could be delivered, and how rapidly Ukrainians could be trained to use them. Some systems may also face interoperability issues with current Ukrainian systems.

European missile defense systems can help defend Ukraine against Russian cruise missile strikes, but the U.S. Patriot is the only NATO system that can defend against Russian ballistic missile attacks. Most Russian strikes involve cruise missiles that can be intercepted by European systems, such as the SAMP/T. However, outside of Italy and France, the SAMP/T has not been sold to a country since a 2013 purchase by Singapore. Ukraine is also using the Norwegian-produced NASAMS and the German IRIS-T systems. Although U.S. systems—notably the Patriot system—make up only a part of Ukrainian air defense, a U.S. cutoff would leave holes in Ukraine’s defenses.

Another area in which Europe cannot completely replace the United States is intelligence. U.S. satellite intelligence has played an important role in Ukraine’s targeting of Russian assets both inside Ukraine and beyond its borders. A U.S.-led fusion center in Wiesbaden, Germany, has provided location data on priority Russian targets in Ukraine to the Ukrainian military daily since early 2022. The inclusion of U.S. intelligence in the Ukrainian kill chain—and the improvement of analysis and integration through constant practice—has increased the speed with which Ukraine can find and attack Russian military assets. This intelligence relationship contributed to the destruction of Russian forces at Sievierodonetsk in May 2022 and the defense of Kharkiv in May and June 2024, among other important successes.

U.S. intelligence has also played a significant role in Ukraine’s campaign against Russian-occupied Crimea, in which U.S. and UK officers oversaw “virtually every aspect of each strike, from determining the coordinates to calculating the missiles’ flight paths,” and in Russia itself. For example, the Central Intelligence Agency (CIA) provided vital information to Ukraine on a munitions depot in Toropets, Russia, in late 2024. The ensuing Ukrainian attack destroyed up to 240 tons of explosive material, according to one independent estimate. The U.S. role in Ukrainian attacks in Russia is murky—the CIA must request specific carve-outs authorizing it to play a role in each strike in Russia—but the United States has at least enabled several high-profile strikes against Russian territory since mid-to-late 2024.

In the instance of a cutoff, U.S. staff could transfer their management of logistics to European allies, but this would not be an easy transition. In NATO and via the U.S. European Command, the United States has managed the massive logistics effort to get equipment into Ukraine, and European officials would need time to build up their expertise. An abrupt U.S. cutoff would disrupt the flow of non-U.S. aid to Ukraine.
 

4. What Could Ukraine Produce on Its Own?

Since the 2022 Russia invasion, Ukraine’s domestic defense industry has increased its production capacity and advanced its capabilities. Ukraine currently produces 30 percent of the country’s weapons domestically. This includes cruise missiles, drones, tanks, infantry fighting vehicles, armored personnel carriers, ammunition, and communications systems. Ukraine has also begun plans to establish joint ventures with Germany’s Rheinmetall to manufacture artillery ammunition, France’s Thales to expand innovation on air defense, radar, and electronic warfare, and has discussed similar possibilities with Poland.

The most notable improvement Ukraine has made is the explosion of its drone industry, which produced nearly 2 million drones in 2024. Drones have been a defining feature of combat along the frontlines. In addition, Ukraine’s long-distance unmanned aerial systems (UASs) have successfully struck oil facilities in Russia, and its sea drones have struck Russian naval assets in the Black Sea.

Ukraine has also greatly increased domestic production of artillery and mortar ammunition. Between 2023 and 2024, Ukrainian production increased by 150 percent, from 1 million rounds annually to 2.5 million. The country’s defense industry currently employs 300,000 people and consists of 500 private and state-owned companies.

Despite its improvement, Ukraine still relies on foreign assistance for 70 percent of its military equipment and faces several barriers to expanding its domestic capabilities. Many of Ukraine’s domestically produced systems rely on components from other countries, making Kyiv reliant on foreign supply chains. Ukraine does not produce adequate numbers of surface-to-air missile defense systems, which are critical in the current conflict. It also relies on China for drone and jamming equipment parts, which has restricted exports of these items. Russia has also made efforts to attack Ukraine’s weapons production facilities. Motor Sich, an engine manufacturer, and Antonov, an aircraft producer, reported total combined damage of $601 million to their facilities from 2022 to 2024.

Replacing U.S. intelligence support would be particularly difficult. Although Ukraine has its own assets and has dramatically improved its ability to use U.S. precision assets based on its own intelligence, the loss of U.S. sensing and analytic capability would mean an overall decrease in Ukraine’s ability to gather and process battlefield information.

5. What Would Be the Impact on Ukrainian Morale?

A U.S. cutoff could hinder Ukrainian morale and the country’s will to fight. Failing to consider Ukraine’s will to fight in pre-war assessments contributed to analyst’s overconfidence in a swift Russian victory. Currently, Russia and Ukraine are fighting a war of attrition with the hope that the other side will be exhausted: Morale is thus a critical variable on both sides.

Assessing will to fight is notoriously difficult, and predicting how adversity will affect a nation’s or force’s morale is even more so. In some cases, dire straits appear to stiffen a nation’s spine—as occurred during the Blitz unleashed by Nazi Germany against the United Kingdom in World War II. In others, it triggers collapse—as seen in Afghanistan in 2021.

In the short term, a U.S. cutoff would bolster morale on the Russian side and probably undermine it in Ukraine, though not necessarily severely. Moscow may reason that time is on its side and that the military balance will shift steadily in its favor. Ukraine, in contrast, may feel abandoned and thus more willing to make diplomatic sacrifices it would not have otherwise considered. It is, however, unlikely that the withdrawal of U.S. aid will do such harm to Ukrainian morale that it triggers a collapse of the country’s armed forces or government. Ukraine fought with limited U.S. aid in the critical early days of the war, and there is no reason to think it would rather lay down arms than do so again.

6. How Would Russia’s Allies Respond? 

Just as the United States and Europe bolstered Ukraine over the last three years, Russia is not alone. China has provided significant economic support, including numerous components for weapons systems, as well as a market for Russian energy exports. North Korea has provided around 15,000 troops (and suffered almost 5,000 casualties), helping make up for deficiencies in Russian manpower, while Iran has provided drones and short-range ballistic missiles. 

A U.S. cutoff of aid to Ukraine is likely to embolden all of these countries. In the short term, they may increase aid to Moscow, believing that Ukraine is on its last legs. The cutoff also sends a signal that the United States will not support allies facing invasion and that U.S. alliances, even NATO, are far from rock solid. This may not lead to additional aggression from these states in the near term, but it will affect their calculations when weighing attacks or coercion against U.S. allies and partners.

7. How Would a Cutoff Alter the Balance of Forces in Ukraine?

A halt in U.S. aid will shift the strategic initiative even further toward Russia. The ebb and flow of U.S. aid has impacted both sides’ battlefield strategies before, with Russia trying to take advantage of the ebbs. Russia’s 2024 Kharkiv offensive, for example, seems to have resulted from Russian assessments of a “window of opportunity” created by a decrease in U.S. arms supplies. Although Ukraine beat back the offensive, it only did so following a major change in how the United States allowed it to use advanced U.S. weapons systems and targeting intelligence, enabling deeper strikes into Russia.

Russia is likely to increase its offensive activity against the Ukrainian front line if its military perceives Ukrainian stockpiles to be low in the wake of U.S. cuts. These offensives are hardly guaranteed to succeed—Russia’s current pace of advance has slowed to a crawl—but even failed offensives will continue to bleed Ukraine’s smaller military. At the very least, the grinding war of attrition will continue, and Ukraine will have less firepower with which to counter Russia’s manpower advantage.

The more immediate damage to Ukraine’s combat effectiveness would be the result of suspended intelligence sharing. Ukraine has its own assets and has dramatically improved its ability to use U.S. precision assets based on its own intelligence, but the loss of U.S. sensing and analytic capability will mean an overall decrease in the ability to gather and process battlefield information. Despite the ingenuity and skill of Ukrainian soldiers, they cannot destroy what they cannot locate. U.S. intelligence has made the Ukrainian targeting cycle much faster, and speed often determines who lives and dies on the battlefield. If a Russian vehicle or formation has moved by the time Ukraine has processed the targeting intelligence, no number of precision strike systems can destroy it. Shortfalls in intelligence sharing during Ukraine’s 2022 Kherson and 2023 Melitopol offensives demonstrate what happens when U.S. intelligence is not available: Media reporting suggests that Ukraine did not fully exploit its initial victories in part because the United States did not share satellite imagery of the battlefield.

Ultimately, setbacks to Ukraine would depend on the scope and scale of a U.S. cutoff and the degree to which Europe is able to fill the void. Continuing the transfer of systems already in the pipeline, allowing Europe to purchase U.S. weapons, permitting intelligence sharing, and a major effort by Europe to bolster production would make a U.S. cutoff more manageable for Ukraine. A more complete cutoff would make it far more likely that Ukraine would suffer battlefield losses.

In the event of significant shortfalls in intelligence and military supplies, Ukraine is likely to adapt. It has demonstrated some ability to find important targets without U.S. support and has displayed important tactical innovations in its use of drones, battlefield software, and adapted military hardware. Doctrinal and technological improvements have turned the tide of wars before, although efforts to predict how or when this will occur yield nothing better than educated guesses—it is the testing of those new concepts and technologies in combat that proves their game-changing effects. Successful adaptation might also limit the loss of effectiveness associated with an end to U.S. aid, but successful adaptation is difficult both to achieve and to predict.

If the United States undertakes a full or extensive cutoff of aid to Ukraine, Russia’s armed forces will probably not immediately sweep across the battlefield to victory. But an aid cutoff would render Ukraine’s long-term prospects dependent on three highly unpredictable factors: Europe’s ability to bring new military production online, Ukraine’s ability to increase its combat power through innovation, and the speed at which both can occur. Even if Europe and Ukraine can fill the gaps left by U.S. production, intelligence, and know-how, they will have to do so before Russia can take advantage of the likely dip in Ukrainian fighting power to irreversibly turn the tables on Kyiv and undermine the successes that the past three years of U.S. support have made possible.

Iselin Brady is an intern with the Warfare, Irregular Threats, and Terrorism Program at the Center for Strategic and International Studies in Washington, D.C. Daniel Byman is the director of the Warfare, Irregular Threats, and Terrorism Program at CSIS. Riley McCabe is an associate fellow with the Warfare, Irregular Threats, and Terrorism Program at CSIS. Alexander Palmer is a fellow with the Warfare, Irregular Threats, and Terrorism Program at CSIS.