When U.S. President Joe Biden greenlit Ukraine’s use of longer-range, U.S.-provided missiles known as ATACMS to strike targets deep inside Russia this week, he crossed what Russia has deemed a red line. The decision came after months of pressure from Kyiv, European allies, and Ukraine-supporting members of the U.S. Congress who blamed Biden’s foot-dragging for Ukraine’s cascading losses.
Biden’s gambit will fail for the same reason his broader Ukraine policy has: It ignores the conflict’s basic math. Given limits on U.S. stockpiles and defense production and Ukraine’s manpower constraints—all readily apparent from the war’s outset—there has never been a sustainable way for Washington to fuel its partner to total victory over Russia.
When U.S. President Joe Biden greenlit Ukraine’s use of longer-range, U.S.-provided missiles known as ATACMS to strike targets deep inside Russia this week, he crossed what Russia has deemed a red line. The decision came after months of pressure from Kyiv, European allies, and Ukraine-supporting members of the U.S. Congress who blamed Biden’s foot-dragging for Ukraine’s cascading losses.
Biden’s gambit will fail for the same reason his broader Ukraine policy has: It ignores the conflict’s basic math. Given limits on U.S. stockpiles and defense production and Ukraine’s manpower constraints—all readily apparent from the war’s outset—there has never been a sustainable way for Washington to fuel its partner to total victory over Russia.
Now, as U.S. President-elect Donald Trump prepares to make good on his pledge to end the war in Ukraine, he should learn from Biden’s mistakes. The most realistic path to peace requires Ukraine and its backers to adopt a defense-only strategy focused on protecting the country’s remaining territory rather than pressing forward with new offensive strikes.
It has been foreseeable from the war’s early days that Kyiv would run out of people to serve in its army. With a much smaller population than its Russian adversary and a conscription age for men of 27 (now lowered to 25), Ukraine benefited initially from a surge in patriotism that brought in new recruits. As this effect wore off and high casualty rates set in, manpower shortages quickly became a limiting factor on Kyiv’s war effort and its capacity to absorb and productively deploy U.S. aid as it arrived.
Kyiv’s inability to spare personnel from the front lines constrained the length and reach of Western-led training programs intended to teach Ukrainian soldiers how to use new U.S. equipment. As a result, for much of the war, only parts of Ukraine’s army have been able to operate the most advanced U.S. tanks, air defense, and artillery systems, including the High Mobility Artillery Rocket System used to fire ATACMS. Flooding Ukraine with hardware that its military could not use effectively or repair easily was never going to tip the balance toward Kyiv. In fact, Ukraine was often more successful fighting with the Soviet-style systems to which it was accustomed.
Case in point, during its vaunted 2023 counteroffensive, Ukraine was well supplied with advanced U.S. and European military hardware and stockpiles of munitions. But it could only muster about 50,000 soldiers, including nine U.S.-armed and -trained brigades, against Russia’s 350,000 soldiers, who were entrenched behind layered defensive lines and fortifications such as “dragon’s teeth” and minefields. Without enough people, Ukraine’s surge stood little chance at reclaiming all of its lost territory, no matter how much offensive materiel was available.
Today, Ukraine’s manpower shortfalls are deeper, exacerbated by the arrival of North Korean forces in Russia’s Kursk region. With its army badly outnumbered and barely able to hold its defensive positions, Ukraine’s small supply of ATACMS will not reverse the battlefield momentum, even with expanded permissions. Ukraine’s ability to fire ATACMS deeper into Russia will, however, renew escalation risks. Inside Ukraine, Russia is already seeking retribution by intensifying its airstrikes on civilian and military targets. Beyond this conflict, Russia could undermine U.S. interests in other ways, for example by further expanding its campaign of sabotage in Europe or accelerating arms flows to Houthi rebels in the Middle East.
In addition to personnel constraints, other math problems continue to work against Ukraine. The shallowness of U.S. arsenals and weaknesses in the U.S. defense industrial base have restricted what military assistance the United States can provide and for how long. It was obvious in February 2022 that U.S. stockpiles—already stretched thin by a global web of military commitments—could not live up to Biden’s “as long as it takes” promise and that its peacetime defense industrial base could not work fast enough to be of much near-term help.
For instance, to meet Ukraine’s insatiable need for 155 mm ammunition—estimated to be at least 4 million shells per year—Washington quickly burned through what it could pull from its own reserves, including those located in Israel and South Korea. New production has increased to almost 1 million shells per year, but this is still only 25 percent of Ukraine’s requirements.
Similar gaps existed for air defense missiles and other systems. Ukraine estimates it needs thousands of Patriot missiles per year to protect civilian infrastructure and military targets, but the United States is also running low on this critical munition and can only produce 550 of these per year. In the case of ATACMS, the constraints are just as acute. The United States has finite supplies of this longer-range missile, and even putting at risk its own military readiness and pushing other allies and partners to the back of the line, the United States cannot provide Ukraine the volume of materiel it would need to shift the balance of power on the ground.
The math of the conflict was never on Kyiv’s side. As Trump prepares to assume office, he should adopt a strategy that corrects the insolvency of Biden’s approach. Some, including members of Congress and of Trump’s emerging national security team, have argued that the best way to get Russian President Vladimir Putin to agree to negotiations is to raise the pressure on Russia, by taking the “handcuffs” off Ukraine. But the United States cannot surge the weapons needed for such a scheme, and even if it could, Ukraine does not have the manpower to take advantage of them.
Instead, the next administration should push Ukraine to adopt a defense-only strategy. This approach would focus all of Ukraine’s and Washington’s resources on protecting the country’s remaining territory, with the ultimate aim of stopping Russian advances and opening space for diplomacy. Rather than expending effort trying to fend off Russian and North Korean forces in Kursk or conducting strikes inside Russia or behind Russian lines in Ukraine, Kyiv would instead prioritize exclusively defensive investments and operations.
First among these would be building layered defensive lines with well-protected trenches, fortifications, and barriers. It would also include obstacles, such as tank traps, and both anti-tank mines and the anti-personnel mines recently authorized by the Biden administration. If built effectively, strong defensive lines of this sort, backed up by short-range artillery and a fleet of small drones, could halt Russian advances, reducing the payoff of continued fighting and making a settlement more appealing for both parties.
Kyiv has recently made some moves in a defense-focused direction, and its soldiers on the eastern front are making progress in hardening their positions and creating obstacles to slow further Russian gains. But their efforts have not yet been rapid or widespread enough, in part due to distractions such as holding territory in Kursk and launching long-range drone strikes inside Russia. Washington has not helped either, offering aid packages that do not clearly incentivize a narrow defensive focus and sometimes—as with the expanded ATACMS permissions—push Ukraine in the opposite direction.
Ultimately, stalemate alone will not be enough to convince a determined Russian regime, which currently possesses the upper hand, to agree to just any negotiated settlement. Difficult concessions by Ukraine and the United States will also be required. Along with ceding territory, these would likely include some steps already floated by Putin and members of the Trump team, for instance taking NATO membership for Ukraine off the table. It might also involve ending certain sanctions and offering a road map for reintegrating Russia into multilateral institutions. Many of Ukraine’s and Europe’s maximalist conditions—for example, Russian war reparations to rebuild Ukraine—will likely also have to be discarded.
Russia, too, will have to make some allowances to sell the settlement to Kyiv and its Western backers. Some realistic options include plans for continued Western defensive military aid to Ukraine, as Vice President-elect J.D. Vance has suggested; provisions for European military forces based in Ukraine and along the border between Ukrainian- and Russian-held territory; and Ukraine’s eventual integration into the European Union, which has not been a deal-breaker for Putin thus far.
The price of this path toward peace will, therefore, be high. But the alternatives are unsustainable and likely even more costly. Even Ukraine’s supporters increasingly recognize that it has little chance of reclaiming its lost territory militarily and begrudgingly accept that the war is likely to end in a dissatisfying land-for-peace arrangement. With its military position weakening by the day, a longer war does not favor Kyiv but instead likely means more Russian territorial advances in the east, more Ukrainian causalities, and more economic destruction. This would leave Ukraine in an even weaker bargaining position down the road. A near-term settlement is likely to offer Kyiv the best terms, even if they are far from what many had hoped. There is no escaping this uncomfortable reality. Numbers, after all, don’t lie.
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