As President Donald Trump and America’s European allies consider options to end the war in Ukraine, one of the most important—but trickiest—issues has been that of devising credible, post-conflict “security guarantees” for Ukraine. Without such guarantees, the logic goes, Ukraine will never be confident enough to make the painful political and territorial concessions that will likely be required to end the war, and only with a Western commitment to come to Ukraine’s defense in the future will it be able to prevent future Russian aggression.
But devising credible guarantees for Ukraine is no easy task. For understandable reasons, the United States and its European allies have been reluctant to take Ukraine into NATO, which would imply a willingness to go to war with Russia that for better or worse does not exist. Some have suggested avoiding this problem by extending a NATO guarantee but taking comfort in the fact that the treaty doesn’t technically require the use of military force in case of an armed attack on an ally—it only says each ally will take “such action as it deems necessary” to restore and maintain security if an armed attack occurs. But relying on that literal interpretation of the treaty for Ukraine could dilute the traditional understanding of Article 5 for other members, a bad tradeoff.
Even President Joe Biden, strongly committed to U.S. global leadership, standing up to Russia, protecting the people of Ukraine, and defending the principle of nonaggression, was not willing to risk a direct conflict with Russia over Ukraine. President Trump, never a big fan of alliances, is surely even less ready to do so, and even he might not be able to get such a commitment ratified by the U.S. Senate if he tried. Given that no NATO members have been willing to directly confront Russia militarily while Russia has been brutally attacking Ukraine over the past three and a half years (and extending back to 2014 in Crimea and the Donbas), it is hard to imagine making a credible commitment that they would do so against theoretical Russian attacks in the future.
The Imperative of Strong National Forces for Ukraine
In the absence of NATO membership, the Trump administration has been discussing fallback options with its European allies, which could include a limited European troop presence potentially backed by U.S. airpower, but without a formal security guarantee. After his summit with Ukrainian President Volodymyr Zelensky and European leaders in Washington on August 18, Trump was only willing to make vague commitments of U.S. “involvement” and “coordination,” with Europeans “in the first line of defense.”
But without greater and more concrete U.S. involvement than that, those options may create the worst of all worlds: enough European forces on the ground to be at risk, but not enough to deter Russian attacks. In the days following the summit, Trump ruled out deploying U.S. troops to Ukraine, and a top Pentagon official confirmed the U.S. role would be “minimal.”
Nor can Ukraine count on the sort of security assurances that were given in the 1994 Budapest Memorandum, which committed its signatories – the United States, Russia, and the United Kingdom along with Ukraine – to respect Ukraine’s sovereignty and existing borders and to refrain from the use of force against Ukraine. Russia violated those assurances when it invaded Ukraine in 2014 and in 2022, and no Ukrainian leader could rely on them or any similar formulations in the future.
The bottom line is that in the current circumstances the only credible guarantee for Ukraine is to have the strongest possible national forces—we know the Ukrainians are willing to fight—which the United States and its European allies would support with money, training, intelligence, and arms.
The Taiwan Relations Act Precedent
Fortunately, there is a precedent for such an arrangement—one put in place long ago for Taiwan. When the United States switched its recognition of China from the Republic of China (ROC) in Taiwan to the People’s Republic of China (PRC) in Beijing in 1979, it had to abandon the defense treaty it had in place with the island since the 1950s.
After recognizing the PRC, the United States couldn’t make a formal commitment to defend Taiwan from China, but it did want to provide Taiwan the defense support necessary to deter an invasion. The solution came from Congress in the form of the Taiwan Relations Act of 1979 (TRA), which has been in place – and has helped deter war with China – ever since.
The TRA did not commit the United States to coming to the defense of Taiwan militarily. But it did make clear Washington would “consider any effort to determine the future of Taiwan by other than peaceful means, including by boycotts or embargoes, a threat to the peace and security of the Western Pacific and of grave concern to the United States.”
It also made clear that the United States would “make available to Taiwan such defense articles and defense services in such quantity as may be necessary to enable Taiwan to maintain a sufficient self-defense capability” and that it would “maintain the capacity of the United States to resist any resort to force or other forms of coercion that would jeopardize the security, or social or economic system, of the people on Taiwan.”
Substitute “Ukraine” for “Taiwan” in the above language, and you could have a model for how the United States and its allies could make Ukraine more secure without writing checks they cannot cash or diluting existing treaty commitments.
The TRA, and the “strategic ambiguity” at its heart, has been much maligned over the years, with some critics calling for it to be abandoned in favor of formal security guarantees and others calling on Washington make clear it would not defend Taiwan. But it has also helped to ensure, for nearly a half a century, that Taiwan would have the national means to defend itself in the face of Chinese aggression, reinforced by the possibility that the United States would get directly involved (and by a set of assurances from the U.S. executive branch, including that the United States would not formally recognize Chinese sovereignty over Taiwan nor set a date for ending arms sales). Initially controversial, the TRA has become a mantra for U.S. Taiwan policy, and to this day underscores the enduring bipartisan U.S. commitment to the security of Taiwan.
Translating the TRA Model to Ukraine
At the July 2024 NATO summit, of course, the United States signed a bilateral security agreement with Ukraine, which underscored the U.S. interest in Ukraine’s security and committed the United States to build and maintain Ukraine’s deterrent capability, much like the TRA. That agreement built on multiple G7 leaders’ statements over the years committing the group to provide enduring defensive support to Ukraine while imposing severe costs on Russia in the case of future Russian aggression. But all those declarations were during the Biden administration, whose support for Ukraine was not in doubt, and Congress never voted on a bill (the Stand with Ukraine Act) proposing to endorse the commitments.
A new law, backed by the Trump administration and passed into law by a Republican-led Congress, would help alleviate the questions that have since been legitimately raised about the U.S. defense commitment to Ukraine. The prospect of a new law, particularly if coupled with a commitment not to recognize Russian sovereignty over Ukrainian territory, could also provide Kyiv the incentive it will need to agree to, and politically defend, an eventual peace deal. And the prospect that such a law could help deliver that peace deal would make it more likely that otherwise reluctant members of Congress would support it.
Some argue that given the risks and opportunity costs involved in such a commitment, instead of bolstering our support for Ukraine the United States should reduce it in order to free up resources to contain China, but that argument has it exactly backwards. Allowing Russia to get away with blatant, illegal aggression against a democratic U.S. partner in a strategic region of the world without paying a high price could lead China to think it could get away with the same in its neighborhood, whereas imposing severe costs on Russia for its action would remind Beijing that aggression carries a high price. A TRA-like commitment to Ukraine would underscore the American determination to do so without running the risks of a formal, treaty-based defense guarantee.
There are obvious differences between the situations in Ukraine and the Taiwan Strait. These include the fact that the United States is more likely to participate directly in the defense of Taiwan because of perceived U.S. interests there—notably Taiwan’s role in containing Chinese threats to other U.S. allies in the region and as a supplier of the world’s most advanced semiconductors—which bolsters the deterrent effect of “strategic ambiguity.” But the lower likelihood of direct U.S. military intervention in Ukraine also makes a TRA-like commitment to Ukraine more valuable rather than less. In the absence of a credible threat to come to Ukraine’s defense with U.S. troops, a more concrete U.S. commitment to provide Ukraine defensive support and sustain costs on Russia could make a significant difference to Moscow’s calculations, including by undermining its assumptions that U.S. support for Ukraine will eventually wane.
In an ideal world, the United States would take Ukraine into NATO and back up its ironclad treaty commitment to its security with the threat of direct U.S. military force, just like for other NATO members. But we don’t live in that world, and pretending we do and not meaning it would be worse than nothing. The Taiwan model could help square a circle that can otherwise not be squared.
