‘Security Guarantees’: Ukraine’s Backdoor NATO Membership Plan?

The war in Ukraine, now entering its fourth brutal year, remains a geopolitical flashpoint that tests Western unity and resolve. 

Kyiv’s urgent calls for NATO membership, repeatedly denied by prominent American political leaders—including President Donald Trump—have only heightened the strategic ambiguity surrounding Ukraine’s future. 

As Trump and his advisors assert that Ukraine will never be admitted to NATO under his watch, Kyiv is left grappling with a precarious security situation.

This impasse raises a critical question: Could Western “security guarantees” offered outside formal NATO membership serve as a “backdoor” Article 5 pledge?

Understanding Article 5 and NATO Membership

Article 5 of NATO’s founding treaty remains the cornerstone of transatlantic security, mandating collective defense—an attack on one member is considered an attack on all. 

Formal NATO membership, therefore, carries immense strategic weight, a fact well understood by Ukraine, which has sought such a binding commitment as protection against Russian aggression. 

Yet, Trump’s categorical refusal—echoed by many within his political circle—reflects a correct hesitance borne out of fear of direct confrontation with Russia.

Exploring Informal Security Guarantees for Ukraine

Despite these public refusals, a scenario emerges in which Ukraine might receive robust security guarantees, mirroring many aspects of NATO’s Article 5, without actual alliance membership. In fact, this is what seems to have created the conditions for the now famous Oval Office argument between U.S. and Ukrainian leaders last week. 

If enacted, and to be clear, we are still a long way from such a scenario on the U.S. side, such guarantees could be designed to assure Kyiv of substantial Western assistance in the event of renewed aggression by Moscow, albeit without explicitly triggering NATO’s formal collective defense mechanisms. 

This “backdoor” commitment would represent a delicate balancing act, offering deterrence against Russian belligerence while avoiding a direct NATO-Russia confrontation.

Historical Precedents and Models

Historically, informal security guarantees have precedents. 

The United States, for example, has extended such assurances to countries like Taiwan, providing substantial defensive support without formal treaty obligations that explicitly mandate military intervention.

The Taiwan Relations Act, though intentionally ambiguous, has successfully maintained deterrence against Chinese aggression for decades. 

Similarly, security guarantees for Ukraine could be modeled to offer sufficient ambiguity to deter Russia without necessarily committing NATO to an automatic, formalized military response.

Challenges and Risks of Informal Guarantees

Yet, the practical implementation of such guarantees would face significant challenges, again, if even the Trump Administration would ever get onboard with the idea. 

First and foremost is credibility: to deter Moscow effectively, these guarantees must be robust and believable. 

Ambiguity, while useful diplomatically, risks creating loopholes that adversaries could exploit. Russia, observing past hesitations among Western nations, might calculate that any informal pledge falls short of an ironclad guarantee, thereby diminishing deterrence.

Moreover, internal cohesion within the Western alliance presents another hurdle. Even within NATO, a clear consensus on Ukraine’s status and support level remains elusive. European allies have varying degrees of risk tolerance regarding conflict with Russia, influenced by geography, economic ties, and domestic political pressures. Achieving unanimous support for informal security commitments could prove difficult, reducing their practical effectiveness.

Critics argue that informal guarantees would create precisely the scenario NATO has sought to avoid—ambiguity leading to potential miscalculations. Moscow might interpret vague Western promises as a bluff or a half-hearted commitment, potentially emboldening rather than deterring aggressive behavior. This risk of misinterpretation and escalation underscores the inherent danger in “backdoor” guarantees, especially when confronting a nuclear-armed adversary like Russia.

The Case for Flexible Security Assurances for Ukraine

Nevertheless, proponents assert that clear yet flexible security assurances might strike the ideal balance—enough to reassure Ukraine and dissuade Russian aggression, yet cautious enough to avoid direct conflict.

Such guarantees could include explicit commitments to supply advanced military technology, real-time intelligence support, enhanced training, and economic backing during crises, collectively raising the cost of Russian aggression without explicitly committing Western troops.

The Future of Ukraine and Security 

Ultimately, the concept of a “backdoor” Article 5 is not without precedent or merit, though it remains inherently risky. No wonder Team Trump seems skeptical. 

For Ukraine, such an arrangement might offer immediate reassurance and deterrence value without provoking Russia as directly as formal NATO membership. Yet, these assurances must be carefully calibrated to avoid miscalculations and to ensure alliance unity and commitment. Kyiv’s security hinges on the credibility of Western resolve—formal or otherwise.

Donald Trump speaking with supporters at a campaign rally at the Phoenix Convention Center in Phoenix, Arizona.

In the ongoing geopolitical chess match over Ukraine, Western powers, particularly the United States under leaders like Trump, face critical decisions. The complexity and potential peril of informal security guarantees underscore the urgency of clear, coherent policies that navigate between deterrence and escalation. The stakes for Ukraine—and for broader European security—remain extraordinarily high, requiring innovative yet cautious strategies that secure Kyiv without igniting wider conflict.

The Bottom Line

My gut tells me any security guarantees, at least for now, would come only from Europe. Could President Trump be persuaded otherwise? I hope that Trump lets Europe take the lead on Ukraine and any security guarantee promises from here on in, providing an intelligence and arms sales channel but never committing to any combat deployment like in NATO’s Article 5.  Stay tuned. 

About the Author: Harry J. Kazianis 

Harry J. Kazianis (@Grecianformula) is Editor-In-Chief of 19FortyFive and President of Rogue States Project, the think tank arm of the publication. Kazianis recently served as Senior Director of National Security Affairs at the Center for the National Interest. He also served as Executive Editor of its publishing arm, The National Interest. Kazianis has held various roles at The National Interest, including Senior Editor and Managing Editor over the last decade. Harry is a recognized expert on national security issues involving North & South Korea, China, the Asia-Pacific, Europe, and general U.S. foreign policy and national security challenges. Kazianis previously served as part of the foreign policy team for the 2016 presidential campaign of Senator Ted Cruz. Kazianis also managed the foreign policy communications efforts of the Heritage Foundation, served as Editor-In-Chief of the Tokyo-based The Diplomat magazine, Editor of RealClearDefense, and as a WSD-Handa Fellow at the Center for Strategic and International Studies (CSIS): PACNET.