President Donald Trump is fond of flexibility. Unperturbed by changing course, he prefers not to be pinned down by past precedent or by his own promises. Although he has pledged to end the war in Ukraine quickly, and although Washington has just signed a deal with Kyiv granting the United States a share of future revenues from Ukraine’s minerals reserves, Trump could decide to walk away from the country entirely if he does not get the peace settlement he craves. A final text of the minerals deal has not yet been made public, but there is no indication that it includes security guarantees for Ukraine. As commander in chief, Trump can minimize U.S. support for Ukraine abruptly and dramatically.
But a Ukraine shunted aside by the United States would not be a Ukraine abandoned. After three years of war, dozens of countries now support Ukraine’s increasingly capable military. No ally can replace the United States, but all of them make a difference: it is not within the power of the United States to end the war by pulling out. Although Ukraine will struggle to hold the line without U.S. support, Russia has no easy path to victory. The real risk of a precipitous American withdrawal of support is not that Ukraine will immediately collapse, but that individual European countries might lose the political will to stand up to Russia.
Should the United States forsake Ukraine, Europe would suffer multiple misfortunes. European leaders would conclude that Washington, having devoted itself to normalizing ties with Moscow, is no longer interested in providing the credible deterrence it had supplied for decades. They would perceive the Trump administration’s abandonment of Ukraine as the first step toward a post-American Europe, if not a post-American world. Against this backdrop, Moscow may be tempted to scare Europe into submission, and some Europeans might choose appeasement rather than risk Russia’s wrath.
ON THE DEFENSIVE
The Trump administration is unlikely to endorse another supplemental support package for Ukraine. In a few months, the amount of weaponry and ammunition going from the United States to Ukraine will diminish. Even as Trump seeks economic gain from Ukraine in the form of a revenue-sharing deal, the United States may also curtail or halt the targeting and intelligence support it provides. Although Russia would still struggle to win the war outright, it would not have to worry about losing the war, either. It could lean into its strategy of damaging Ukraine’s civilian infrastructure and terrorizing Ukrainians into leaving the country. Kyiv has the manpower, resources, and support to maintain sovereignty in most of the country, but Russian forces could advance slowly and make territorial gains, fulfilling Putin’s goal of getting four of Ukraine’s regions fully under his control.
Lacking the ability to make offensive gains, Ukraine would find it difficult to resolve the war on its terms. After successfully defending Kyiv in the spring and summer of 2022, Ukraine made daring moves in the south and the east, retaking the city of Kherson and liberating huge swaths of territory in the Kharkiv region. Last July, Ukraine even took a piece of Russian territory in the Kursk region. But over time, Ukraine has exhausted its offensive capabilities, and Russia has gradually pushed Ukrainian forces out of Kursk. Ukraine makes occasional drone strikes within Russia, and its degradation of Russian naval power in the Black Sea has been impressive, but Kyiv lacks the manpower and the materiel to capture large amounts of territory. Ukraine has drifted quietly, almost imperceptibly, from the wide-open war it was fighting in 2022 and 2023 to the defensive war it has been conducting since late 2024.
Without U.S. help, the support of its remaining allies would be crucial to Ukraine. Ukrainian forces have been innovative in their use of drone warfare, and European countries will continue to provide military aid. But Ukraine would suffer from a severe shortage of air defenses, enduring missile strikes across frontlines that would be essentially unprotectable. Kyiv would have to ration ammunition and would lose up-to-the-minute information on the battlefield. Even if the Europeans decide to step up, targeting would be exceptionally difficult without U.S. technology.
Ukraine’s leadership knows what is at stake, and it knows what to expect. Kyiv will have to make difficult choices about which territories are defensible. Between the valor and efficiency of Ukraine’s military and the continuous support from its remaining allies, however, Russia has no real path forward in Ukraine. The loss of life on the Russian side would not cease with American abandonment of Ukraine. The war would remain a strategic blunder for Russia. Even so, that abandonment would greatly burden Europe, call into question Washington’s commitment to its European allies, and likely generate spiraling tensions between Europe and Russia.
A POST-AMERICAN EUROPE
The Trump administration might believe that Ukraine’s destiny has no bearing on the future of the NATO alliance. The reality is that Ukraine is a linchpin of European security. The country is a twenty-first-century laboratory of containment, which has been the tacit transatlantic policy toward Russia since 2022. A U.S. retreat from Ukraine would signal to Moscow that Washington is no longer committed to checking the spread of Russian power in Europe. Seeing a green light, Russia would be tempted to test the foundations of European security, not necessarily through invasion but through intimidation and blackmail.
Russian President Vladimir Putin could target a European Union or NATO member state that he perceives as weak or internally divided; perhaps one of the Baltic countries or Romania. He could invent a crisis, perhaps claiming that a Russian-speaking minority is being persecuted in the country, and communicate a zeal to escalate by, say, demonstrating the reach of Russia’s missiles. If the United States were unwilling to back the targeted country, the larger European powers—France, Germany, and the United Kingdom—would need to get involved. But without the United States, they might not be able to compel Russia to back down. The combined British and French nuclear arsenals are insufficient to deter Moscow from engaging in nuclear first-use blackmail or conventional threats. In the absence of a credible U.S. security umbrella for Europe, Russia would view NATO as a paper tiger.
In a post-American Europe, Moscow would establish a patchwork of individual relationships with European countries, confronting some with territorial threats and gray-zone tactics (such as disinformation campaigns) and rewarding others for their acquiescence with cheap energy. These circumstances could motivate some European countries to embrace neutrality or even partnership with Russia. No longer kept in check by a counterbalancing power such as the United States, Putin could reconstitute a sphere of influence in Europe. And then, the hegemonic transatlantic alliance—the dragon that Russian strategists have been trying to slay since the late 1990s—would be no more.
To be sure, Russia does not have the military capacity to capture much European territory outside Ukraine, and that is most likely not Moscow’s underlying intention. But by terrifying and tempting Europe, Putin could drive a wedge in the transatlantic relationship and undermine the European project.
THE HEART OF EUROPEAN SECURITY
The prospect of a less committed United States instills fear in Europeans. It has already prompted higher defense spending in the EU. But the Europeans, including the United Kingdom, are still unprepared to take full responsibility for their own defense. They do not have the political will to take joint action. They lack the money, the military hardware (especially critical enablers such as intelligence and airlift capabilities), and the command-and-control structures necessary for any joint European defense. These capabilities will not be ready for years, possibly decades, and France’s and the United Kingdom’s nuclear umbrellas, even if extended to other European countries, are no match for Russia. Only the United States can ensure credible nuclear deterrence.
Some European countries, deserted by the United States and lacking a formidable European-only defense alliance, may be cowed into cutting deals with Moscow. They may reestablish trade relations or concede to Russian demands regarding the stationing of European troops and hardware. Europe is already rife with political parties willing to accommodate the Kremlin for short-term gain. And because the desired outcome—Europe’s ability to defend itself without the United States—might take more than a decade to achieve, citizens may be reluctant to vote in politicians promising to invest in defense today.
Even countries willing to stand up to Russia might still be tempted to abandon lengthy joint European defense efforts for the sake of short-term bilateral deals with the United States. Poland has already asked the United States to deploy nuclear warheads on Polish soil instead of in western Europe. Should a race to secure favors from Washington ensue, Trump would relish playing the Europeans against each other. In time, the European security landscape could return to a pre-war hodgepodge of complex and confusing security deals and reassurance treaties, tying some countries to each other while excluding others. Amid the confusion, the emergence of rivalries among European countries is entirely possible. Whether the EU can withstand such developments, or whether it would survive at all without a U.S.-led NATO, is an open question. A brittle and acrimonious Europe would benefit only Russia.
To avert a drift toward division and conflict in Europe, the Trump administration should not consign Ukraine to Europe’s periphery. Nor should it view Ukraine only in economic terms. Instead, Washington should build on the recently agreed-upon minerals deal and commit to Ukraine’s long-term security; a sovereign Ukraine capable of defending itself would help to stabilize the entire region, a core U.S. interest.
Since its independence from the Soviet Union 1991, Ukraine has too often been denied a significant place in Europe’s security architecture. At the 2008 Bucharest NATO summit, the alliance promised Ukraine membership, a promise that was callously forgotten. In multiple rounds of diplomacy in 2014 and 2015, after Russia’s takeover of Crimea and incursion into Ukraine’s Donbas region, France and Germany expended more effort on a cosmetic cessation of hostilities than on solving the underlying problems of regional security. The consequence, some eight years later, was Russia’s brutal invasion, which has sent ripples of insecurity across Europe. Today, the status of Ukraine lies indisputably at the heart of European security.
Without the United States at its side in Ukraine, Europe would face impossible choices. European countries would have to fill gaps in their own security and defense investments, as well as Ukraine’s. Limited resources, or pressure from Washington to moderate relations with Moscow, might induce the Europeans to cut back support for Kyiv, undermining their own long-term security in the process. Moreover, a U.S. abandonment of Ukraine would complicate NATO’s ability to deter Russia. For now, Moscow is tied down in Ukraine and cannot afford to pursue more expansionist undertakings. But should the Trump administration decide that Ukraine does not merit U.S. partnership and cooperation, Putin’s ambitions will only grow—along with the cost of deterring Russia in the future. If Washington abandons Ukraine now, Europe could become the consuming crisis of Trump’s second term.
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