Question for the candidates: How will you reassure allies worried about the credibility of the US security guarantees?

Editor’s note: Sara Moller, an associate teaching professor at Georgetown University and a non-resident senior fellow at the Atlantic Council, suggests that the 2024 US presidential candidates be asked about how they plan to reassure allies who doubt the US readiness to protect them. (This is part of an “experts comment” series of questions for the candidates.)

The US nuclear arsenal is intended not only to ensure national security but also to protect that of its allies—a policy known as extended deterrence. For 75 years, the United States has served as the supreme guarantor of Western Europe’s security, extending its nuclear umbrella to shield NATO members from potential aggression. For nearly as long, it has extended this nuclear pledge to allies in the Indo-Pacific region. In total, more than 30 countries currently benefit from the US nuclear guarantee.

At times, some allies have sought to develop nuclear weapons programs of their own. On those occasions, Washington dissuaded them through an implicit bargain of non-proliferation and extended deterrence in which allies agree not to develop their own nuclear weapons in exchange for further assurances that the United States will protect them.

However, over the years, allied governments have regularly expressed doubts about the credibility of US security assurances. These doubts typically arise either in response to rising threats from regional adversaries, perceived reductions in the US security commitments (either in the form of troop withdrawals or presidential statements), or both. On those occasions, previous US administrations have sought to reassure anxious allies via a mix of political-military measures, including military exercises, deployments, announcements of new or enhanced consultative measures, and official statements.

For example, after South Korean President Yoon Suk-yeol publicly raised the possibility of South Korea acquiring nuclear weapons in early 2023, the Biden administration responded by reaffirming its commitment to enhance extended deterrence efforts against North Korea. A few months later, Washington and Seoul announced the formation of the Nuclear Consultative Group, a new bilateral body aimed at improving information sharing and enhancing dialogue about nuclear threats and plans. In addition to strengthening extended deterrence against North Korea, this new consultative forum also reassures South Korea of Washington’s commitment to its security.

However, the current deterioration of the international security environment and nuclear modernization efforts and increased military capabilities of Russia and China could make it harder for Washington to reassure its allies in the coming years. In Europe, the ongoing Russian aggression against Ukraine and continued nuclear saber-rattling by Moscow, coupled with growing uncertainty about the degree of bipartisan support the continent can expect from Washington in the future, has led some NATO allies to start questioning the nuclear status quo in Europe.

The next US president will face challenging questions from allies regarding the future of the US policy of extended deterrence. While some of the resulting debates will likely echo issues from the Cold War era, other issues raised will be entirely new, owing to the evolving security environment and the emergence of the multiple nuclear challenger problem.

The 2024 presidential candidates, therefore, should be asked the following questions:

• Is the US nuclear arsenal sufficient to protect its allies from Chinese, Russian, and North Korean aggression? If not, how would you recalibrate it so that US nuclear forces can simultaneously deter strikes against the US homeland and against allies in Europe and the Indo-Pacific?
• If asked by Seoul, would you agree to redeploy nuclear weapons onto the Korean Peninsula, more than 30 years after they have been withdrawn?
• In July, Washington and Berlin announced the United States would be deploying intermediate-range missiles to Germany by 2026. If your national security advisors recommended in the future that these be armed with nuclear (instead of conventional) warheads, would you support such a move?
• In light of Russian and Chinese nuclear modernization efforts, will your administration seek to maintain the bargain of non-proliferation and extended deterrence with allies? Or will you move to support allies in developing their own nuclear deterrent capabilities instead, thereby abandoning the US nonproliferation obligations?