Security Guarantees for Ukraine: Models, Issues, and Questions

On Oct. 9, 2025, the Congressional Study Group on Foreign Relations and National Security convened over Zoom to discuss the potential models for, and legal and policy questions surrounding, security commitments to Ukraine. As the United States and its European allies have signaled that they are likely to offer Ukraine security commitments—both to help bring an end to its war with Russia and to deter future Russian aggression—observers have noted that such commitments can take a wide variety of forms, each entailing a distinct set of complex legal and policy considerations. This session explored those different models, ranging from formal treaty-based guarantees to looser political assurances, and the role Congress might play in shaping and overseeing them.

For the session, the study group was joined by two leading experts, whom coordinator Scott R. Anderson led in an initial discussion:

• Eric Ciaramella, senior fellow at the Carnegie Endowment for International Peace and a former National Security Council and intelligence community official focusing on Ukraine; and
• Laura Cooper, former deputy assistant secretary of defense for Russia, Ukraine, and Eurasia.

Background readings circulated before the session included:

• Eric Ciaramella, “The Case for a Binding Security Agreement with Ukraine” Lawfare (Mar. 6, 2024);
• Eric Ciaramella and Eric Green, “Ukraine, NATO, and War Termination,” Council on Foreign Relations (Feb. 2025); and
• “Unpacking Security Guarantees for Ukraine,” Lawfare Daily (Aug. 28, 2025) (podcast).

Ciaramella opened by emphasizing that there is no single, agreed-upon definition of a “security guarantee”; the term lies largely in the eye of the beholder and spans a broad spectrum of form and substance. At the upper end sits NATO, which he described as the “gold standard”—a multilateral commitment ratified by the Senate and backed by decades of joint planning, exercises, and integrated command structures. He cautioned, however, that the strength of the NATO commitment derives less from the text of Article 5 of the Washington Treaty—which is in fact rather vague and leaves parties considerable discretion as to “such action as it deems necessary”—than from the institutional practice and credibility built up around it. He contrasted NATO with the U.S. mutual defense relationship with South Korea and with the support relationship the United States maintains with Israel, including the codified commitment to Israel’s qualitative military edge (QME), which Congress wrote into law in 2008 and which, like the Taiwan Relations Act, anchors an enduring bilateral relationship.

Turning to the legal mechanics, Ciaramella explained that the strongest commitments—those embodied in treaties that have gone through the Senate’s advice-and-consent process—are the most durable but also the hardest to obtain, particularly because commitments to use military force implicate Congress’ own constitutional war powers. He distinguished such treaty commitments from executive agreements and from looser political “assurances,” noting that the Budapest Memorandum of 1994—under which Ukraine relinquished its inherited Soviet nuclear arsenal in exchange for “security assurances” rather than guarantees—illustrates the consequences of vaguer, nonbinding commitments. He observed that more recent arrangements, including the G7 declaration made on the margins of the 2023 NATO summit and the subsequent bilateral security agreements, generally operate at the executive-agreement level, and that it remained unclear into which category the current administration’s approach would ultimately fall.

Ciaramella then surveyed the principal pillars of current and prospective support for Ukraine: ongoing security assistance, intelligence sharing, consultation mechanisms triggered by signs of renewed aggression, and the more contested question of foreign troop deployments. He noted that, apart from the deployment of forces, most of these elements were already in play, with the United States having spent roughly $65 billion in security assistance over three years and European partners contributing comparable sums. He stressed that credible commitments could give Ukraine the confidence to come to the negotiating table and pursue an agreement that might be painful in some respects, and underscored that the architecture of any guarantee should be designed so that a ceasefire is not made wholly contingent on the security arrangements being finalized.

Cooper drew on her recent experience at the Department of Defense to address how these commitments would function in practice, focusing on the hard-power elements and the institutional capacity required to sustain them. She noted that, under the prior administration, support for Ukraine had been delivered largely on an executive-only basis, relying on competent, detail-oriented personnel and periodic supplemental appropriations, but expressed doubt that the executive branch alone could reliably sustain such an effort over the long term. She pointed to legislative proposals as offering a more durable foundation by codifying commitments in law. Both speakers agreed that placing the relationship on firmer statutory footing would lend it greater credibility in the eyes of both Ukraine and its adversary, and that congressional involvement would be essential to ensuring its long-term resilience.

The session then concluded with an open discussion wherein attendees were invited to ask questions or present their own views on some of the issues raised. As with all sessions of the study group, the discussion was conducted under the Chatham House Rule, meaning that statements made there are not for attribution without the permission of the speaker.