Ukraine's security guarantees rest on Putin's calculations, not European wishes

The diplomatic architecture Europe has spent 2025 constructing for Ukraine's security, a 34-nation coalition of the willing, a pledge from 26 countries to put troops on the ground after a ceasefire, rests on a single, uncomfortable premise: none of it functions without the United States. British and French leaders can announce multinational forces until the parliamentary recess, but the logistics, intelligence, air defence and command structures that would make such a force credible are overwhelmingly American. That reality, stark as it is, has been the subtext of every European summit since the Oval Office rupture between Volodymyr Zelenskyy and Donald Trump early in the year.

The guarantee that matters is not European

Ed Arnold, a senior research fellow at the Royal United Services Institute, puts it plainly: Washington's guarantees are the only viable path to peace. Europe's efforts are real, and they have political value, they signal cohesion, they keep the Americans engaged, they create facts on the ground. But the Multi-National Force Ukraine that Emmanuel Macron described in September cannot deploy, sustain or defend itself without US enablers. The 26 nations that signed up know this. So does the Kremlin. The question is not whether Europe wants to guarantee Ukraine's sovereignty; it is whether Europe can. The answer, for now, is no.

This is not a new problem. The 1994 Budapest Memorandum, under which Ukraine surrendered the world's third-largest nuclear arsenal in exchange for security assurances from the United States, Russia and the United Kingdom, was an executive agreement, politically binding but legally toothless. When Russia annexed Crimea in 2014 and launched the full-scale invasion in 2022, the memorandum's signatories held consultations. That was the extent of their obligation. The memory of that failure casts a long shadow over every negotiation in Kyiv, Washington and European capitals today.

What the US is actually offering

The package on the table from Washington is described by US officials as 'platinum standard', a phrase that carries weight in Pentagon corridors but has no treaty definition. It reportedly includes the provision of Tomahawk land-attack cruise missiles with a range of 1,000 km, a capability only four US allies have ever received: the United Kingdom, Australia, Japan and South Korea. Such missiles would allow Ukraine to strike political and military centres deep inside Russia, altering the Kremlin's cost calculus for any future aggression. But the offer comes with an explicit deadline: these terms 'will not be on the table forever'. The administration is pressing Kyiv to accept the deal now, before the political window closes.

Zelenskyy, for his part, has signalled willingness to drop Ukraine's quest for NATO membership, described as 'irreversible' at the 2024 Washington summit, in exchange for these guarantees. That is a substantial concession. NATO membership would have brought Ukraine under Article 5, the collective defence clause. A bilateral US treaty would not. The distinction is not semantic; it is the difference between an alliance commitment backed by 32 nations and a bilateral promise backed by one, however powerful.

The Budapest shadow

The Budapest Memorandum's failure was not merely that Russia violated it. The United States and United Kingdom also failed to treat it as a trigger for automatic military response. They chose consultations, sanctions, and incremental military aid, essentially the same menu deployed since 2014. Zelenskyy's team understands this history. They are demanding a legally binding treaty requiring ratification by both chambers of Congress and presidential signature, placing Ukraine on the same footing as Japan and South Korea. Those treaties, negotiated in the early Cold War, commit the United States to defend its allies with the full range of military capabilities, including nuclear. They have survived changes of administration, shifts in congressional majorities, and evolving strategic priorities because they are law, not policy.

The alternative, a presidential executive agreement, like the Paris Climate Accords or the Iran nuclear deal, binds only the president who signs it. A successor can withdraw with a stroke of a pen. Trump did so with both. If Ukraine's guarantees take that form, they are worth precisely as much as the current president's word, for as long as he holds office. That is not a guarantee; it is a loan.

Article 5 is not a template

Zelenskyy has said the proposed guarantees 'correspond to Article 5'. Trump, en route to the NATO summit in The Hague this summer, replied: "There are numerous definitions of Article 5". He was right. Article 5 was deliberately worded in 1949 to avoid automaticity. It states that an armed attack against one ally 'shall be considered an attack against them all' and that each ally will take 'such action as it deems necessary, including the use of armed force'. The phrase 'as it deems necessary' is the escape hatch. It was written that way because the United States, scarred by two European wars in three decades, refused to cede the decision for war to a collective vote. Every NATO summit since has reaffirmed the clause, but none has removed the ambiguity.

If Article 5 were easily replicable, similar mutual defence treaties would exist worldwide. They do not. The US-Japan and US-South Korea treaties are among the few that approach that level of commitment, and they were forged in the specific crucible of the early Cold War. The United States has provided measured support to Ukraine since 2014, consistently blocked its path to NATO since 2022, and made avoidance of direct involvement a strategic priority. A bilateral treaty that could compel US intervention in a war with a nuclear-armed Russia would be a departure of historic magnitude. Whether Congress would ratify such a treaty, and whether a future president would honour it, is an open question.

The ratification hurdle

Ratification requires a two-thirds majority in the Senate. The current Senate is broadly supportive of Ukraine, but 'broadly supportive' and 'two-thirds for a war commitment' are different thresholds. The House must also pass the implementing legislation. Both chambers have shown willingness to fund military aid, but a treaty obligation is a different order of political risk. Senators from both parties have spent decades avoiding votes that could be framed as sending American troops to fight in Eastern Europe. The Jackson-Vanik amendment, the Magnitsky Act, the Ukraine Democracy Defense Lend-Lease Act, these passed because they imposed costs on Russia or provided materiel, not because they committed US forces to combat.

If ratification fails, the fallback is an executive agreement. That returns the guarantee to the durability of a single presidency. Zelenskyy's hope is that a ratified treaty would give Ukraine a permanent constituency in Congress, a mechanism to influence future appropriations and oversight hearings, ensuring support remains 'strong and united'. That is a plausible theory. It is also a gamble on American domestic politics remaining stable for decades.

Putin's veto

The maxim that 'the enemy gets a vote' is attributed to various generals; its truth is undeniable. While European and Ukrainian diplomats negotiate the architecture of guarantees, and US officials draft treaty language, bilateral US-Russia talks proceed in parallel. Putin has presented a 28-point peace plan demanding a far more expansive European security settlement: limits on NATO infrastructure, withdrawal of forces to 1997 positions, legal guarantees against further enlargement. He has not conceded on his maximalist demands. It remains unclear what Russia will accept, but it is certain that any settlement durable enough to be called peace requires his signature, or at least his acquiescence.

This is the structural asymmetry. The United States can offer Ukraine a treaty. Europe can offer a multinational force. Ukraine can offer concessions on territory and NATO aspirations. But Russia decides whether the war ends. If Putin calculates that a US-Ukraine treaty, even one without Article 5 automaticity, unacceptably constrains his freedom of action, he will continue the war. If he calculates that the treaty's ambiguity, or the likelihood of a future US withdrawal, leaves him room to manoeuvre, he may accept a ceasefire. The durability of any guarantee, in other words, is not written in the treaty text. It is written in the Kremlin's assessment of American resolve.

What happens next

The next inflection point is the US congressional calendar. Treaty ratification cannot proceed in a lame-duck session; it requires the new Congress convening in January 2026. The administration must submit the text, the Senate Foreign Relations Committee must hold hearings, the full Senate must debate and vote. Each step is a venue for amendment, delay, or defeat. Meanwhile, the 'platinum standard' offer expires, deliberately, according to US officials, creating pressure on Kyiv to accept before the terms degrade. Europe's coalition of the willing will continue meeting, planning, signalling. But the force it envisions remains a paper construct without the American enablers that only a ratified treaty, or a sitting president's executive order, can unlock.