Ukraine’s security guarantees have been put in Putin’s hands

Ed Arnold is a senior research fellow for European security at the Royal United Services Institute.

Early in 2025, Ukrainian President Volodymyr Zelenskyy had a severe diplomatic dustup with U.S. President Donald Trump and Vice President JD Vance in the Oval Office. Since then, relations between Washington and Kyiv have swung up and down and back again.

Europe, for its part, reacted to the diplomatic incident with increased efforts to support Ukraine and keep the U.S. onside. In March, British Prime Minister Keir Starmer and French President Emmanuel Macron announced the launch of a 34-nation “coalition of the willing” to strengthen Europe’s role in ensuring Ukraine’s future sovereignty and security. And in September, Macron announced that 26 countries committed to deploying troops on the ground as part of a Multi-National Force Ukraine “the day after the ceasefire or peace.”

However, regardless of Europe’s efforts to support Ukraine, the only thing that really matters is America’s security guarantees, which Zelenskyy must now secure — even if it means concessions elsewhere.

As much as Europe may like to think otherwise, Washington’s guarantees are the only viable path to peace for Ukraine. Europe can’t even deploy its multinational force without U.S. logistical support. And as 2025 draws to a close, the question of Washington’s commitment remains a fundamental factor in efforts to move Russia’s war toward its next phase and, hopefully, a durable peace.

Yet, everything suggests real power lies in Russia’s hands.

Ukraine’s collective memory of the 1994 Budapest Memorandum’s failures — security guarantees that were provided by the U.S., Russia and U.K. so that Ukraine would surrender its Soviet-era nuclear weapons — cast a long shadow over current negotiations. And at this truly perilous moment, Zelenskyy has several points to consider:

First, the Ukrainian president is reportedly prepared to drop Ukraine’s quest for NATO membership — something the alliance had described as “irreversible” at last year’s NATO Summit — in exchange for robust security guarantees, and there are signs these could be forthcoming. So far, the U.S. has offered Ukraine “platinum standard” security guarantees, alongside the caveat that they “will not be on the table forever,” pushing Zelenskyy toward accepting the deal currently on the table.

In addition, there are hopes that these guarantees would include the provision of Tomahawk cruise missiles with a range of 1,000 kilometers — only four U.S. allies have ever been granted Tomahawks in the past. These would allow Ukraine to strike Russia’s political and military centers, thus potentially deterring the Kremlin from resuming hostilities. But while this additional capability would certainly complicate Russian President Vladimir Putin’s decision-making, it’s no silver bullet.

Apart from the guarantee’s technical details, Zelenskyy rightly hopes that unlike the Budapest Memorandum, which was an executive agreement, any commitment would be legally binding, requiring ratification by the U.S. House and Senate — both of which are broadly supportive of Ukraine — and then approval by the president.

Such formal ratification would put Ukraine’s guarantees on similar footing to other U.S. bilateral security treaties with countries like Japan and South Korea.

Alternative vehicles like a presidential executive action, which was used for both the Paris Climate accords and the Joint Comprehensive Plan of Action to limit Iran’s uranium enrichment, are non-binding political commitments, meaning a future president wouldn’t be bound by them. So, if formal ratification is on the table, Zelenskyy will be hoping it provides Ukraine future opportunities to influence Congress and ensure support remains strong and united.

But even then, there are risks. While Zelenskyy has said the security guarantees “correspond to Article 5,” this core alliance commitment is fragile.

On the plane to the NATO Summit in the Hague this summer, Trump mentioned: “There are numerous definitions of Article 5” — and he was right. Article 5 is open to interpretation, and was deliberately worded as such in 1949 to prevent the U.S. from being automatically pulled into a third major war on the European continent. Therefore, it isn’t just a question of the letter of the treaty but also its spirit.

Of course, NATO is far more than just Article 5. Founded on the ashes of World War II, it’s also an alliance built on economic collaboration (Article 2), as well as an individual and collective capacity to resist armed attack (Article 3) . But if Article 5 was easily replicable, then alliances with similar strength would be established all over the world. In reality, mutual security guarantees backed by credible military force are rare.

So it’s questionable whether the U.S. would, in fact, choose to offer a guarantee that could force it to directly intervene in Ukraine, especially considering it’s provided measured support since 2014, consistently blocked the country’s path to NATO since 2022, and made it a priority to avoid getting directly involved in the war.

Finally, it is a maxim of war that “the enemy gets a vote.” So, as bilateral engagements between the U.S. and Russia continue in parallel with European and Ukrainian negotiations, Putin’s position will be important, whether one likes it or not. Russia wants a far more expansive deal with the U.S. on European security — something it clearly demonstrated with its initial 28-point peace plan. And with Putin refusing to concede on his maximalist demands to date, it remains unclear what Russia will accept.

Ultimately, regardless of how strong Zelenskyy believes America’s security guarantee is, its durability may still be based on Putin’s interpretation.