The Ukraine crisis has plunged U.S. and Western relations with Russia toward a post–Cold War low. The damage will continue for some time, especially in the event of a Russian military incursion into eastern Ukraine. Among the victims could be further progress on arms control. Yet arms control is now all the more valuable. It puts important bounds on an increasingly confrontational U.S.-Russian relationship.

The Kremlin’s occupation and annexation of Crimea plus its persisting military pressure on Ukraine have broken a cardinal rule of the post–World War II European order: states should not use force to take territory from other states. The West has responded with sanctions against Russia, and will likely apply additional penalties if Moscow continues to escalate the crisis.

This deterioration in East-West relations caused by Russian actions has already claimed a number of victims, including NATO-Russian cooperation. The U.S. government has frozen a wide range of bilateral contacts with Moscow, as have European governments. Unfortunately, another victim could be further arms control.

Prior to the Ukraine crisis, Washington and Moscow had a full arms-control agenda—including further cuts in strategic forces, limits on tactical nuclear weapons, a resolution of differences on missile defense, and the restoration of a conventional arms-control regime in Europe—though little progress had been registered in the past two years. Russia has shown particularly little interest in new bilateral nuclear-arms reductions, arguing instead for multilateral nuclear arms control, even though U.S. and Russian nuclear forces dwarf those of any third nuclear-weapons state.

Furthermore, the broader downturn in bilateral relations makes pursuing bilateral arms control even more difficult. The U.S. government will put actions on hold that once seemed sensible, such as accelerating its implementation of the New START agreement’s limit on deployed strategic warheads. In the current atmosphere, other proposals for reducing or limiting nuclear weapons will not receive serious hearings in Washington.

The administration, moreover, has to contend with unwise proposals offered as ways to punish the Russians for their actions against Ukraine. Some on Capitol Hill, for example, have suggested that the United States withdraw from New START, which makes no sense for U.S. interests, as discussed in greater detail below.

Others call for reviving the Bush administration’s plan to place ten ground-based missile interceptors in Poland and a supporting radar in the Czech Republic. Russia already does not like U.S. plans to deploy SM-3 missile interceptors in Central Europe (the first are scheduled to be deployed in Romania in 2015, with others to be placed in Poland in 2018). Implementing the Bush plan might make Moscow a tad more unhappy, but the Czechs have said they would not accept the radar, and the troubled ground-based interceptor has not had a successful flight test in six years.

While current tensions make arms control more difficult to pursue, they also underscore the value of arms-control constraints.

The New START caps the number of Russian strategic nuclear forces and provides a significant degree of transparency and predictability. The treaty’s data exchanges, notifications and on-site inspections—all of which have continued to be implemented in spite of the Ukraine crisis—offer assurance that the strategic-nuclear-arms relationship remains bounded, providing an important degree of stability.

What if New START were not in place? The U.S. military and intelligence community would have significantly less information regarding Russian strategic forces. The Pentagon would have to begin making worst-case assumptions.

Russia currently has ongoing building programs for new intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles and ballistic-missile submarines. As U.S. strategic forces are in different stages of their life cycles, U.S. strategic modernization programs will not begin in earnest for another seven to ten years. New START means that the Defense Department, which must now weigh the implications of a more threatening Russian posture for U.S. conventional forces and their deployments, does not have to worry about an increase in Russian strategic nuclear numbers beyond New START’s limits. Instead of spending more on strategic forces—where Russia can build ICBMs more cheaply than the United States can—the Pentagon could fund high-tech conventional systems where the U.S. military has a comparative advantage.

Arms control thus serves to keep the deterioration in relations in check. With New START in place, Washington does not have to worry about a strategic-nuclear-arms race on top of everything else it must deal with regarding Russia.

We should also bear in mind that, during the Cold War, even the most tense periods, arms control provided a key channel for communication between Washington and Moscow. At times, it offered the only working channel of any significance.

Arms control, moreover, often provided momentum to push the broader relationship to a better stage. During the late 1960s, negotiation of the SALT agreements gave a major impetus to détente. Following the suspension of nuclear arms talks in 1983 and a low point in U.S.-Soviet relations, Ronald Reagan and Mikhail Gorbachev used arms control to forge a more cooperative relationship. The negotiation of New START in 2009-2010 helped create conditions in which Washington secured greater Kremlin cooperation on pressuring Iran’s nuclear program and facilitating the supply of American and coalition forces in Afghanistan.

Bilateral arms control currently appears a difficult proposition. There is no question, however, that New START offers a useful degree of stability and predictability in the uncertain times between Washington and Moscow. It provides a channel of communication when other contacts are closing up. And later, when the crisis is resolved, it could provide a means to spur restoration of a more positive relationship.

Steven Pifer directs the Brookings Arms Control and Non-Proliferation Initiative and served as the U.S. ambassador to Ukraine from 1998-2000.