	Introduction

The Comprehensive Nuclear-Test-Ban Treaty, or CTBT, would ban all nuclear explosions. It was opened for signature in September 1996; as of February 2008, 178 nations had signed it and 144 of them had ratified. The treaty might be an issue in the presidential campaign. It is organized around three aspects of how the treaty might affect U.S. security that were prominent in the 1999 debate: the CTBT and deterrence; monitoring and verification; and implications for nuclear nonproliferation and disarmament. At issue, though, is what is needed for deterrence. Can existing weapons be maintained without testing? Can the United States Maintain Existing Warheads Without Testing? Does Deterrence Require New Warheads That Must Be Tested? CTBT opponents see deterrence as dynamic, so that it continues to require new military capabilities that can only be embodied in new weapons that could only be developed with nuclear testing. U.S. conventional forces, the treaty's supporters claim, deter threats from other nations. Since 1999, scientists have made many advances in detection capability that have been widely published. Seismic monitoring entails other arguments. Supporters assert that the treaty would make evasion harder. But clandestine testing offers advantages: an open weapons development program could spur rivals to launch their own program, so a nation wanting to develop nuclear weapons might prefer to keep its intent unknown; a nation that withdrew from the treaty would lose access to IMS data, which could help it evade detection; a nation that withdrew from the treaty to conduct nuclear tests might face the same penalties as one that conducted clandestine tests and was caught cheating; and a nation might prefer to stay in good standing with the international community for as long as possible in order to delay any sanctions. Opponents argue that the treaty would weaken deterrence and that nonproliferation and disarmament are not linked. In this view, the extent of proliferation is about what it would be had the United States ratified the CTBT; this nation has made progress on nuclear nonproliferation despite not having ratified the treaty; the weapons labs have supported 12 annual assessments that nuclear weapons remain safe and reliable despite the lack of testing; and the strategic balance favors this nation whether or not Russia or China has tested clandestinely. The Treaty's Technical Contributions to Nonproliferation

CTBT supporters hold that the treaty would make specific technical contributions to nuclear nonproliferation. To maintain credibility, opponents believe, the U.S. nuclear deterrent must respond to changing conditions. As a result, it is argued, steps toward disarmament are essential for nonproliferation. CTBT opponents, however, see no logical linkage between nonproliferation and disarmament. They note that the United States has taken a great many steps to counter proliferation, many since 1999. Opponents note that even if the United States were to ratify the CTBT, it would still not enter into force, so they see the attempt to gain Senate advice and consent as an exercise in futility, especially given that the Senate rejected the treaty in 1999 by a vote of 48 for, 51 against, and one present—far short of a two-thirds majority. Some supporters hold that U.S. ratification would help secure international cooperation with the United States by symbolizing a U.S. turn toward multilateralism. Appendix A. The resolutions of ratification were also subject to a second declaration:
mindful of the commitment of the United States, the Soviet Union and Great Britain in the Limited Test Ban Treaty of 1963 and in the Non-Proliferation Treaty of 1968 to seek the discontinuance of all test explosions of nuclear weapons for all time and of the commitment which shall be legally binding on the Parties upon ratification of the Treaty on the Limitation of Underground Nuclear Weapons Tests [the TTBT] to `continue their negotiations with a view toward achieving a solution to the problem of the cessation of all underground nuclear weapon tests,' the United States shares a special responsibility with the Soviet Union to continue the bilateral Nuclear Testing Talks to achieve further limitations on nuclear testing, including the achievement of a verifiable comprehensive test ban.
The Comprehensive Nuclear-Test-Ban Treaty would ban all nuclear explosions. It was opened for signature in 1996. As of March 2008, 178 nations had signed it and 144 had ratified. To enter into force, 44 specified nations must ratify it; 35 have done so. The Senate rejected the treaty in 1999; the Bush Administration opposes it. The United States has observed a nuclear test moratorium since 1992.
There have been many calls worldwide for the United States and others to ratify the treaty. Many claim that it would promote nuclear nonproliferation; some see it as a step toward nuclear disarmament. Several measures have been introduced in Congress regarding the treaty; it might become an issue in the presidential election.
The U.S. debate involves arguments on many issues. To reach a judgment on the treaty, should it come up for a ratification vote in the future, Senators may wish to balance answers to several questions in a net assessment of risks and benefits.
Can the United States maintain deterrence without testing? The treaty's supporters hold that U.S. programs can maintain existing, tested weapons without further testing, pointing to 12 annual assessments that these weapons remain safe and reliable, and claim that these weapons meet any deterrent needs. Opponents maintain that there can be no confidence in existing warheads because many minor modifications will change them from tested versions, so testing is needed to restore and maintain confidence. They see deterrence as dynamic, requiring new weapons to counter new threats, and assert that these weapons must be tested.
Are monitoring and verification capability sufficient? "Monitoring" refers to technical capability; "verification" to its adequacy to maintain security. Supporters hold that advances in monitoring make it hard for an evader to conduct undetected tests. They claim that any such tests would be too small to affect the strategic balance. Opponents see many opportunities for evasion, and believe that clandestine tests by others could put the United States at a serious disadvantage.
How might the treaty affect nuclear nonproliferation and disarmament? Supporters claim that the treaty makes technical contributions to nonproliferation, such as limiting weapons programs; some supporters believe that nonproliferation requires progress toward nuclear disarmament, with the treaty a key step. Opponents believe that a strong nuclear deterrent is essential for nonproliferation, that nonproliferation and disarmament are unrelated, and that this nation has taken many nonproliferation and disarmament actions that the international community ignores.
This report presents a detailed, comprehensive discussion of the treaty's pros and cons from a U.S. perspective. It contains an appendix outlining relevant history. It will be updated periodically with views from protagonists. CRS Report RL33548, Comprehensive Nuclear-Test-Ban Treaty: Background and Current Developments, by Jonathan Medalia, tracks current developments.