An intercontinental ballistic missile launch, Vandenberg Air Force Base, California, August 2017
Ian Dudley / Reuters

Just days before it was due to expire, the United States and Russia extended the New START treaty—the only major arms control agreement left between the two powers. Its expiration would have marked the first time since 1972 that the nuclear arsenals of Washington and Moscow were not subject to some form of agreed limitations. The five-year extension, however, is a one-time event. U.S. President Joe Biden now faces the question of what should come next.

The welcome extension of New START comes at a worrying moment. Although the United States and Russia have nowhere near the number of nuclear weapons they possessed at the height of the Cold War, both countries are again in the midst of an arms race. Over the past decade, each side has developed new missiles, bombers, submarines, and capabilities to shoot down satellites. Other countries, including China and even North Korea, are warming up, too.

This renewed competition traces its origins to 2001. In the wake of the September 11 terrorist attacks, U.S. President George W. Bush announced that Washington would withdraw from the 1972 treaty limiting missile defenses, a step he argued was necessary to defend the United States against a rogue nuclear strike. In the years that followed, Russia and China responded with campaigns to modernize their nuclear arsenals, fearing that new American capabilities would leave them vulnerable in ways that Washington could exploit.

If Biden wants to slow this arms race, he will need to accept limits on the U.S. missile defense systems that drive it. Such restrictions will be politically hard to swallow, but they are not without precedent. When the United States first began working with Moscow to end the Cold War arms race, both sides agreed to start by limiting missile defenses. If Biden is to address the contemporary escalation underway today, he will need to do the same.

Deterrence and Defenses

An implicit assumption in early thinking about nuclear deterrence was that only a nuclear weapon could threaten another nuclear weapon. It took more than one warhead to reliably destroy a missile in a silo, so if both sides had about the same number of weapons, neither had enough to disarm the other in a surprise first strike. Numerical parity—no matter the actual number of weapons—was, almost by definition, stable. 

In the late 1960s, however, that assumption came under technological assault. The United States and the Soviet Union began deploying new weapons that complicated the old models of deterrence. The single most destabilizing development was the antiballistic missile (ABM) system. 

An instrument for shooting down attacking missiles might sound like an entirely defensive capability. Both sides quickly realized, however, that ABM systems profoundly altered the nuclear calculus. Under conditions of parity, if an aggressor were to strike an adversary and knock out its nuclear missiles, some of those weapons would inevitably survive, allowing the recipient to return the favor. But what if the aggressor had an ABM system? Then, when the victim struck back with the remains of its arsenal, the ABM system could “mop up” any missiles the initial attack had missed. Under these conditions, a first strike might make strategic sense.

If Biden wants to slow this arms race, he will need to accept limits on U.S. missile defense systems.

The two superpowers tried to neutralize this problem by acquiring new defenses that drove an already costly arms race to new heights. Declassified documents show that, for a time, the United States allocated more than 100 Minuteman ground-based missiles—about a tenth of its force at the time—plus an unknown number of Polaris submarine-launched missiles, solely to destroying a pair of modest Soviet defensive sites near Moscow and Tallinn, Estonia.

Eventually, however, the Johnson administration surmised that the Soviets would make a similar calculation and send the conflict spiraling out of control. Limiting defenses would therefore be an essential first step to constraining the nuclear arms race. Ultimately, Washington was able to persuade the Soviets of the wisdom of this approach, and in 1972, Soviet leader Leonid Brezhnev and U.S. President Richard Nixon signed the ABM Treaty. The agreement limited each country to two missile defense sites (later reduced to one each) with 100 interceptors apiece. Moscow and Washington no longer had to stay ahead of each other’s defenses, so both were eventually able to reduce their offensive nuclear forces.

The Arms Race Revives

After the Cold War, the United States judged that “rogue states” could still threaten it with ballistic missiles, so it continued to develop modest systems designed to counter them. Republicans and Democrats spent the 1990s sparring over the need to pursue such defenses, while Russia and China watched warily. Finally, in 2002, Bush pulled out of the ABM Treaty, declaring that the United States needed new systems to address emerging threats from states such as North Korea. So began a new phase in a global arms race.

Russia responded to Washington’s gambit by dusting off projects designed in the mid-1980s to defeat the Reagan administration’s never realized “Star Wars” program. These included doomsday torpedoes, nuclear-powered cruise missiles, hypersonic gliders, superheavy intercontinental ballistic missiles (ICBMs), and antisatellite weapons. Russian President Vladimir Putin unveiled many of these programs in March 2018 with an explicit nod to U.S. missile defense policy. “During all these years since the unilateral U.S. withdrawal from the ABM Treaty,” he told Russian lawmakers, “we have been working intensively on advanced equipment and arms.” China, too, has modified its nuclear forces in profound ways. Over the past two decades, Beijing has developed a new generation of ICBMs, placed multiple warheads on existing missiles, tested a hypersonic glider to deliver strategic weapons, and demonstrated an antisatellite system. Both countries, of course, are investing in their own defenses.

U.S. officials initially expressed surprise at these developments—especially Russia’s outlandish new weapons—but the purpose of such tools is no mystery. They are designed to evade and defeat U.S. missile defenses: more warheads can overwhelm defensive systems; antisatellite weapons could destroy the orbiters on which defenses depend; more powerful missiles can fly over the South Pole, where the defenses can’t intercept them. Neither Beijing nor Moscow is likely to restrict its new weapons unless Washington places corresponding limits on the defenses that such weapons were meant to defeat. If the Biden administration is serious about reviving arms control agreements with Russia and bringing China into the fold, it will need to compromise.

Limiting Defenses

Successfully limiting defenses will be far more complicated than merely reviving the 1972 ABM Treaty. Even when that treaty’s limits were in place, the United States and other countries continued developing systems for countering short-range missiles. By the 1990s, it was clear that these so-called theater defenses, particularly in quantity, were sophisticated enough to undermine the purpose of the ABM Treaty. That trend continues today. In mid-November 2020, for instance, the U.S. Department of Defense for the first time tested a sea-based theater defense system, the SM-3 interceptor, against an ICBM-class target. Although the test was highly scripted, it largely erases any useful demarcation between strategic defenses targeting long-range ballistic missiles and those designed to protect against short-range missiles armed with conventional warheads.

The loss of an effective divide between different defensive systems means the Biden administration can’t merely revive the ABM Treaty and call it a day. Instead, it will have to adapt the treaty’s general approach. The parties could, for example, limit themselves to a single national or “homeland” defense system with a cap on the number of land-based interceptors and radars, much as they did under the ABM Treaty.  Doing so would freeze the new defensive arms race at a manageable level: the United States currently plans to deploy 64 ground-based interceptors at its primary site in Alaska, with another four in California. Moscow’s ABM system also has about 68 interceptors. Deployments of this size are too small to threaten either Russia’s or the United States’ nuclear deterrents.

The existence of nuclear weapons entails the risk of nuclear danger.

Alternatively, the United States could agree to freeze its defenses at current levels in exchange for a commitment from Russia and China to verifiably suspend testing and deploying new nuclear capabilities designed to defeat U.S. defensive systems. It seems unlikely that Moscow and Beijing will agree to abandon all such programs, but slowing the arms race by eliminating some and limiting others would still be worth doing.

Theater defenses present a more difficult problem. Systems such as the U.S. SM-3 or Russian S-400 are widely available, are often deployed with regular military units, and are, at least in principle, able to intercept some ICBMs. It is extremely hard to imagine any verifiable way to limit the number of such systems. Biden’s team will have to find other approaches to help minimize the threat these defenses pose to strategic stability. Limiting testing against ICBM-class targets or restricting the areas in which countries can deploy theater defenses might manage the threat, especially if such a policy is accompanied by transparency and confidence-building measures.

Facing Vulnerability

Limiting missile defense systems will be unpopular in the United States, especially among Republicans in Congress. The argument against such restrictions has always been that to accept them is to acquiesce to vulnerability. Without defenses, there is no prospect of victory in a nuclear exchange and no U.S. military superiority—only a common mortal danger shared with Russia, China, and even North Korea.

But the simple fact is that the existence of nuclear weapons entails the risk of nuclear danger. Deterrence does not function without the fear of catastrophe, and no country gets to opt out, not even the United States. The Biden administration would do well to level with the American public about what it means to base U.S. security on nuclear deterrence. An arms control agreement limiting missile defenses would most likely need to be a formal treaty, subject to review by the Senate. The Biden administration would therefore need to expend considerable political capital negotiating such an agreement and getting it through the Senate. Even then, a future president could demolish that work—just as partisans have sought to repeal the Affordable Care Act and torpedo the Iran nuclear deal.

In the end, a successful nuclear policy, like climate change or mass shootings, may be simply too difficult for the U.S. political system to handle. The country’s institutions may be too broken and its politics too poisonous. But addressing the Cold War arms race felt impossible, too. After the Berlin and Cuban nuclear crises, few observers would have imagined that generals, senators, and presidents would ever come to see defenses as dangerous and work with the Soviets, of all people, to change tack. For a time, such arguments did indeed fall on deaf ears, as both sides built ever-larger nuclear arsenals. Eventually, however, both governments came to see that building tens of thousands of nuclear weapons was an unsustainable means of deterrence, and a different approach became possible. To get there, leaders had to be wise enough to see the opportunity—and brave enough to seize it.

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  • JEFFREY LEWIS is a Professor at the Middlebury Institute of International Studies at Monterey.
  • More By Jeffrey Lewis