Concerns over verification and compliance are a refuge for skeptics of arms control. These concerns can be substantive as well as overdramatized. No treaty is risk-free, and no monitoring regime is foolproof. Will a powerful cheater be called out, even if discovered? And what then? No treaty seeking to tame the Bomb offers the prospect of automatic penalties. Arms-control advocates have countered with the standard of “effective verification,” which basically means that militarily significant violations will be discovered in sufficient time to take remedial action.

The outcome of these debates over nuclear testing have typically hinged on Moscow’s behavior during and prior to the debate, the perceived benefits of the treaty at hand, and public perception of the President’s stewardship of U.S. national security. The 1963 Limited Test Ban Treaty was an iffy proposition until the Senate roll was called. The Comprehensive Test Ban Treaty probably will be as well. For the CTBT, China’s behavior will matter as much as Moscow’s.

The particulars of verification matter. If these concerns appear to be outlandish, while benefits appear to be tangible, skeptics will be on the defensive. This was the case during debate over the LTBT, which stopped atmospheric tests, when skeptics argued that the Soviet Union might still test nuclear weapons in deep space, behind the moon, or at the bottom of Lake Baikal. In testimony before the Senate Foreign Relations Committee in 1963, Secretary of Defense Robert McNamara offered this rebuttal: “The Soviet Union could obtain no major results by testing in the atmosphere and deep space or underwater without incurring high risk of detection and high risk of identification” According to the Pentagon’s math, multi-megaton weapons (a greater concern at the time than low-yield tests) would have to be tested 20 million miles from the earth to evade detection – or 80 times further away from the Moon.

A minority of the Senate – insufficient to scuttle the LTBT — was not persuaded by McNamara’s arguments. Robert Byrd, a Democrat from West Virginia, grew to become a towering figure in the United States Senate, as well as a supporter of nuclear arms and risk reduction. Early on in his Senate career, Byrd thought differently about arms control. During the debate over the LTBT, he offered this critique:

I think we are underrating Soviet cunning and the Soviet determination to outwit us. On the other hand, I think we are overrating the Soviet fear of being caught in a violation and the Soviet respect for world opinion…. I contend that when dealing with the Communists, we must apply the maximum standards and must allow no loophole for evasion, for so long as there is a single loophole, the Communists will find it and use it.

South Carolina Senator Strom Thurmond, then a Democrat, felt the same way, arguing, “The art of concealment always runs ahead of the art of detection.” Thurmond worried about a peculiar evasion scenario. He asked, “What would keep Russia from shifting her scientists, equipment, and personnel to the Chinese side [of the border] to carry out nuclear work?”

These arguments didn’t carry the day because they seemed far-fetched, and because the perceived benefits of a ban on atmospheric testing appeared to be so valuable and pressing. The Director of the Arms Control and Disarmament Agency, William Foster, framed the decision this way:

Weighing the risks involved in a treaty against the value of the test ban in the reduction of the risks of a continued, intensified, and extended arms race, we have come to the conclusion that a nuclear test ban treaty is in our national interest.

The LTBT did not, in fact, have an appreciable impact on the arms race, since robust testing programs continued underground. The treaty did, however, end the public health hazards associated with atmospheric testing and helped to downsize the yields of nuclear weapons.

The next negotiating step, which took eleven more years, placed a threshold on the yields of underground tests at 150 kilotons. Grave reservations were again raised about the benefits the Kremlin could derive from cheating under the 1974 Threshold Test Ban Treaty – claims that were, at best, a stretch. These concerns were, however, given credence by the limitations of seismic monitoring capabilities during the 1970s and the wide bands of uncertainty surrounding the actual yields of Soviet tests. Uncertainty levels were magnified further by a lack of understanding of the geology at Soviet test sites. The U.S. Senate’s hold on the TTBT’s ratification, sixteen years in duration, was eventually broken by creative, joint experiments at test sites – experiments that indicated a systematic overestimation by the U.S. intelligence community of Soviet nuclear test yields.

Six years after the threshold treaty was ratified in 1990, negotiations on the Comprehensive Test Ban Treaty came to a close, a treaty that will take longer than the TTBT’s sixteen years to enter into force. Once again, grave concerns have been raised by treaty skeptics about what the Kremlin might gain by cheating. Now concerns hinge over tests with yields of perhaps ten or a few hundred tons of TNT, compared to the TTBT’s threshold of 150,000 tons of TNT.

Monitoring capabilities have advanced considerably. The CTBT provides a global network of hundreds of distributed facilities and sensors of various kinds to warn of noncompliance at extremely low yields. U.S. national technical means of test ban monitoring are reportedly better. A ban on nuclear testing has never been harder to evade and the benefits of evasion ever never been so slight. No treaty has met the standard of effective verification more completely than the CTBT. Even so, a Senate vote on the CTBT will probably be a cliff-hanger. As with the TTBT, creative supplemental monitoring measures near test sites might be in order to convince two-thirds of the Senate to consent to ban nuclear testing completely.