Why It Matters

A Congressional Research Service (CRS) report on U.S. extended deterrence, updated July 10, has raised alarm about a potential weakening of America's nuclear commitments to over 30 allies and partners worldwide. The Trump administration's 2026 National Defense Strategy omitted any explicit mention of extended deterrence, instead stating that allies and partners would "take primary responsibility" for their own defense with "critical but more limited U.S. support." Some Members of Congress have expressed concerns about this shift and allies' potential interest in acquiring independent nuclear weapons, moves that could undermine the nonproliferation framework the U.S. has spent decades building.

The Big Picture

Since the Cold War, U.S. extended deterrence has served a dual purpose: deterring adversaries like Russia, the People's Republic of China, and North Korea while simultaneously reducing allies' incentives to develop independent nuclear arsenals. The nonproliferation logic depends on allies believing the U.S. will actually use nuclear weapons on their behalf.

The software of assurance includes declaratory policy, joint planning, consultations, and exercises. Former U.S. officials stressed in a 2023 congressional hearing the importance of tending to this software of ally and partner assurance in addition to the hardware of U.S. capabilities. The exercises enable allies to ascertain the credibility of both U.S. defense commitments and potential U.S. use of nuclear weapons.

Congress has acted legislatively to shore up regional nuclear capabilities. Section 1640 of P.L. 118-31 (the fiscal year 2024 National Defense Authorization Act) directed the Department of Defense to establish a major defense acquisition program for a nuclear-armed sea-launched cruise missile (SLCM-N), with the Navy initiating procurement in 2024.

Recent developments underscore the urgency. The North Atlantic Treaty Organization (NATO) has sought to strengthen deterrence capabilities since Russia's 2022 invasion of Ukraine. In July 2025, the United Kingdom and France pledged to deepen their nuclear cooperation and coordination through the Northwood Declaration. Officials in Canada, Sweden, Japan, South Korea, and Australia have all publicly debated nuclear weapons issues, signaling underlying anxiety about the credibility of U.S. protection.

The Bottom Line

Allies' belief in U.S. nuclear commitment can erode, and when it does, they respond by requesting additional security assurances or by developing independent or cooperative nuclear weapons capabilities. Congress provides authorization and appropriation of funds and oversight of U.S. government programs relevant to U.S. extended deterrence policies, and may oversee U.S. engagement with allies and partners, including efforts to assure allies and partners of the credibility of U.S. defense commitments.

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