By Michael Poznansky

January 5, 2024

Foreign Affairs


One of the chief justifications for sending military aid to Ukraine turns on deterrence. Proponents of Western support contend that it is essential for showcasing resolve. The United States and its allies, the argument runs, need to demonstrate to the world, and especially to Chinese President Xi Jinping, that they are willing to put muscle and resources behind efforts to combat unchecked aggression. But a growing chorus of voices argue that continued support to Ukraine is detracting from the real threat—namely, a Chinese invasion of Taiwan. All this assistance, they claim, is depleting valuable resources needed to deter an attempted takeover and defeat China should a war occur.

Framing the debate this way obscures a fundamental but uncomfortable truth: prioritizing one form of credibility can undermine the other. One camp privileges the “would” part of the deterrence equation—does China, or any adversary for that matter, believe that the United States would respond militarily to aggression? The other camp prioritizes the “could” part—does China believe that the United States could respond militarily if necessary to aggression? Both are invoking credibility, but they are talking about different things.

These distinctions matter because of opportunity costs. Doing more to demonstrate resolve in Ukraine today might undermine the United States’ physical capacity to respond to crises tomorrow, even if it wanted to. Alternatively, husbanding resources in the present to preserve capabilities might increase the United States’ physical capacity to respond to future crises but reduce the perception by rivals that it actually would. In short, deterrence can fail in two discrete ways: rivals believe that Washington would respond but can’t or that it could but won’t.

The first step in wrestling with potential tradeoffs between bolstering resolve and bolstering capabilities is to identify them. In a world of finite resources, policymakers will have to make tough choices about what to allocate, where, and for how long. These decisions will only grow more salient as the White House and Congress continue to debate funding to Ukraine and how to deal with China and Taiwan. Ultimately, however, policymakers should prioritize resolve. They should privilege the priceless asset of reputation while spending what they can to improve capabilities, maintaining the flow of aid to Ukraine despite the downsides.


Two years into the war in Ukraine, proponents of continued aid to the country argue that the United States and its allies must stand firm against Russian aggression for the sake of deterring rivals. “The credibility of the U.S. deterrent is only as strong as our actions,” Jack Reed, the Democratic senator from Rhode Island who chairs the Senate Armed Services Committee, argued in October. “Our would-be partners around the world are also watching closely at what we are doing. Will we have their backs if they are attacked? We must show that we are a

steadfast ally, not hamstrung by the whims of fringe politicians.” Senior Taiwanese officials have made similar arguments. In May, Hsiao Bi-khim, then serving as Taiwan’s representative to the United States, told an American audience, “International support for Ukraine is . . . essential in affirming the credibility and reliability of the United States and your allies.”

But as the war in Ukraine has dragged on, critics of continued aid are arguing that the United States must prioritize military assistance to Taiwan to deter a Chinese invasion and defeat one if it occurs, even if it comes at the expense of helping Ukraine. Seeing Taiwan and Ukraine as competing over a limited pool of American aid, some congressional Republicans believe that the former must win out over the latter. In May, two Republican foreign policy hands, Elbridge Colby and Alex Velez-Green, wrote that the United States must focus its “resources on Taiwan’s defense against China, by far the United States’ strongest rival, while relying primarily on European allies to defend against a weakened Russia.”

Both of these competing arguments touch on dynamics relevant to deterrence. Whether Xi believes that the United States would come to the defense of Taiwan, or at least provide it with the resources needed to defend itself through requisite military assistance, is critical. At the same time, it also matters whether Xi believes that the United States has the capacity to provide the necessary resources. Both dynamics are about credibility—the credibility that one has the will to act and the credibility that one can actually do so.

In a world of finite resources, policymakers must come to terms with painful tradeoffs between these twin goals. Devoting scarce supplies to bolster resolve may reduce the capacity to respond to crises elsewhere. Conversely, jealously guarding military supplies to preserve as much capability as possible can undermine perceptions of resolve more broadly. Many in the resolve camp and the capabilities camp, however, are in denial about the tradeoffs with respect to Ukraine, but in different ways. Proponents of aid to Ukraine claim that the United States can do it all. Skeptics of it hold that there are no reputational consequences for abandoning Ukraine. But both are overstating their case.


Although they would be loath to admit it, those in the resolve camp are essentially arguing that the United States can do it all. The basic logic is that Washington can continue supporting Ukraine with military assistance while also preparing for potential conflict in Asia. Remarks made last August by William LaPlante, a top Pentagon official, are emblematic of this view. The secretary of defense and the chairman of the Joint Chiefs of Staff review “every item that is decided and taken from the U.S. stock and provided to the Ukrainians,” LaPlante claimed. If those officials think that removing a given item would have “any impact” on readiness or “increases risk,” he continued, the materiel will not be handed over.

The reality, however, is more complicated. As a Center for a New American Security report has noted, although there are important differences between the kinds of weapons that the United States is providing to Ukraine and the types of weapons that would be needed to stymie a Chinese invasion of Taiwan, there is certainly some overlap. This is especially true in the case of

air defense systems of various kinds—capabilities that Ukrainian President Volodymyr Zelensky has pleaded for.

There is even more overlap once one considers the types of weapons Taiwan would need to continue on the fight following a successful Chinese landing. Although the kinds of weapons the United States would need to defend an initial air and sea assault are relatively distinct from those now being sent to Ukraine, it’s a different story when it comes to the weapons the Taiwanese would use to counter Chinese forces on the island itself. These weapons include a variety of missiles and missile systems, such as ATACMS, Javelins, Patriots, and Stingers. Thanks in part to Ukrainian demand, their supplies are increasingly limited.

There are already signs of competition between Taiwan and Ukraine over certain assets. In 2022, for instance, Taiwan had to buy additional HIMARS—a multiple rocket launcher—to compensate for delays in Paladin mobile howitzers, a weapon the United States provided to Ukraine. Increasingly, the arms Washington and its allies are sending to Ukraine are the very ones Taiwan wants most: not just HIMARS but also Abrams tanks, F 16 fighter jets, and ATACMS. The backlog in delivery of U.S. weapons to Taiwan—which has grown to over $19 billion—predates Russia’s invasion, but Western support to Ukraine has exacerbated the problem.

There is another wrinkle when it comes to arming Taiwan: speed is of the essence. Once hostilities broke out over the island, it would mostly be too late to do much, since the United States and its allies would have great difficulty sending weapons to the Taiwanese. So there is an urgent need to stockpile relevant weapons now. But as Mark Cancian of the Center for Strategic and International Studies has found, many of the weapons needed, including portable missiles, take years to produce, even if the defense industry worked at surge capacity. Supply chain problems create more bottlenecks, and some essential components for weapons—such as the engines for certain missiles—are produced by a single manufacturer.


If those in the resolve camp are not fully coming to terms with the tradeoffs of their preferred strategy, the same is true of the capabilities camp. Many of these critics of aid to Ukraine overlook the effect that their preferred approach would have on perceptions of American resolve, including in the very region they are most interested in, Asia. Some even deny the existence of any tradeoff at all, contending that resolve, reputation, and credibility are ephemeral. Writing in Foreign Policy, Rajan Menon and Daniel DePetris claimed, “What the U.S. government may or may not do in one region of the world tells us next to nothing about what it might do in another.”

Scholars have spent decades trying to understand whether and how reputations for resolve form and what relevance they hold for future crises and decision-making. Although there are many nuances, recent research suggests a few things. Most important, reputations for resolve matter. Showing signs of being irresolute can signal weakness that adversaries take note of. Put differently, past actions inform perceptions of future actions, especially when the two scenarios are reasonably analogous. This is especially true for individual leaders.

These insights have major implications for questions about how arming Ukraine could affect perceptions of the United States’ resolve generally and its willingness to defend Taiwan specifically. First, it stands to reason that if Washington had never supported Ukraine’s defense in the first place, Xi might not have concluded that it was simply safeguarding scarce resources that may be needed for Taiwan, as skeptics would seem to suggest. Instead, he might have concluded the United States lacked the resolve to commit money and arms and risk escalation to resist unprovoked aggression.

Perhaps more important, whether or not the skeptics like it, the United States has been supporting Ukraine since the start of the war. Prematurely abandoning it would not only increase the odds of a Russian victory but send a signal that the United States lacks the willpower to endure a protracted fight. Giving up would raise questions about whether a future U.S. president could sustain expensive military assistance beyond an initial honeymoon period. It would raise even more doubts about whether the United States would actually intervene in the event of a war with Taiwan. If the United States can’t even sustain its indirect involvement in Ukraine, then why should Xi expect it to muster the courage for direct involvement in Taiwan? Even if Xi believed the United States would participate directly, he might conclude it would do so only briefly.

Cutting bait and getting out of Ukraine now in the name of safeguarding resources would also be particularly damaging given the innumerable public statements that U.S. officials have made about why defending Ukraine is essential for protecting the rules-based order. Washington has hyped the stakes of Ukraine. Abandoning a country that was the victim of unprovoked aggression from a revisionist power that has been identified as a core threat would be a far more consequential act than withdrawing from Afghanistan in 2021, a move that marked the end of nearly two decades of counterinsurgency in a strategically marginal region.


No matter what policymakers decide about Ukraine, there will be tradeoffs. The central question, then, is which of two options is preferable. Should the United States keep aiding Ukraine, at least for the time being, both to help resist Russian advances and to bolster resolve, even if it comes at some cost to preparedness in Asia? Or would it be better to safeguard resources for Taiwan, even if the United States takes a hit to its reputation for resolve? There are no perfect answers, but there are good reasons why policymakers should opt for the former course.

First, it is at least possible to devote additional resources to shore up the United States’ defense industrial base, whose deficiencies are largely responsible for prospective shortfalls in weapons platforms and munitions of various kinds. To compensate further, Washington can enlist partners and allies. What no amount of money can buy is resolve. Convincing adversaries that the United States has the fortitude to stand up to unprovoked aggression is linked to the actions it takes in Ukraine.

Fortunately, there are encouraging signs that at least some of the limitations in the supply of weapons are being addressed. In 2023, the Department of Defense created the Joint Production Accelerator Cell, a new part of its acquisition office tasked with “building enduring industrial

production capacity, resiliency, and surge capability for key defense weapon systems and supplies.” Moreover, the National Defense Authorization Act that Congress passed in December authorizes the Pentagon to issue multiyear contracts while procuring munitions. In the past, it could typically do so only when buying large weapons such as ships and airplanes, but the change gives defense contractors greater confidence that the Defense Department will buy key precision-guided munitions and therefore incentivize increased production of them.

With respect to allies, Germany, Norway, the United Kingdom, and other European countries have pledged to ramp up the production of weapons for Ukraine. In December, Finland announced that it will boost production of ammunition to support Ukraine for the foreseeable future. Polish Prime Minister Donald Tusk, elected in December, has promised to increase military assistance to Ukraine after the previous Polish government threatened to curtail certain kinds of assistance.

Another reason why policymakers should prioritize resolve is that the United States has global commitments and reputational stakes beyond China. Prematurely abandoning Ukraine to preserve resources for Taiwan could embolden other adversaries. It might, for example, signal to Iran and North Korea that the United States does not have the appetite to support the victims of aggression once a conflict becomes protracted, or at the very least that it cannot defend more than one country in one region at a time. All this could encourage further adventurism. By continuing to help Ukraine resist Russian aggression, the United States can send a powerful signal to a broader range of rivals: unprovoked aggression will not go unpunished.