Lt. Gen. Robert P. Ashley, Jr., the director of the Defense Intelligence Agency, has stated that Russia “probably is not adhering to its nuclear testing moratorium.” Its activities likely violate the U.S. understanding that the Comprehensive Test Ban Treaty (CTBT) bans testing to a “zero yield’ standard. This report adds a new impetus to calls for the U.S. to formally ‘unsign’ the CTBT.

It is impossible to say for certain whether or not Russia is violating the CTBT because while the CTBT bans explosive nuclear testing, it does not define that term. The U.S. interpretation is that the CTBT bans testing to a “zero yield” standard – because the CTBT bans “any nuclear weapon test explosion or any other nuclear explosion” -- but that is only the U.S. interpretation.

The fact that the CTBT has no agreed interpretation and is therefore substantively meaningless is hardly its only fatal flaw . Even if the U.S. “zero yield” standard was universally accepted, it is unverifiable in practice. Under Secretary of State for Arms Control and International Security Ellen Tauscher, a CTBT supporter, acknowledged in 2011 that a “country might conduct a test so low [in yield] that it would not be detected.”

The wider problem with the CTBT is that it is not possible to make progress on arms control that advances U.S. and allied security, is verifiable and enforceable, and is negotiated with partners who comply with their obligations. The reason why this is impossible is that, as the U.S.’s 2018 Nuclear Posture Review puts it, the world environment today “is characterized by continuing significant non-compliance with existing arms control obligations and commitments, and by potential adversaries who seek to change borders and overturn existing norms.” While the CTBT is multilateral, the Nuclear Posture Review then goes on to point the finger specifically at Russia, saying that it has cheated on the Intermediate-Range Nuclear Forces Treaty (INF) and “is either rejecting or avoiding its obligations and commitments under numerous agreements.”

The Senate has already considered and rejected the CTBT. In 1999 it received only 51 of the 67 senatorial votes needed for approval. This overwhelming defeat made clear that, notwithstanding later statements by both the Clinton and Obama administration, the CTBT had no future in Senate.

Observers might expect that, after the Senate rejection, the CTBT would simple disappear or be automatically returned in disgrace to the White House. But that is not how the U.S. treaty process works. The CTBT remains in the Senate and on the calendar of the Senate Foreign Relations Committee, nominally waiting for another vote but in practice a zombie.

If the administration concludes that Russia has in fact been violating the U.S. interpretation of the CTBT by conducting nuclear tests of any size, it should move to ‘unsign’ the CTBT. Observers might expect that a treaty would have no legal effect on the U.S.’s policy and conduct until it receives the Senate’s advice and consent, but this is not how treaties work. When the president signs a treaty, the U.S. accepts that it is under an obligation not to take actions that defeat what is known as the treaty’s ‘object and purpose.’

The precise meaning of this phrase is often debated, but it implies that the U.S. cannot take new actions that are clearly incompatible with the treaty. ‘Unsigning’ is a formal process that, in effect, removes the U.S. signature from a treaty and thereby eliminates any U.S. obligation to abide by the treaty’s object and purpose. Like any nation, the U.S. can unsign a treaty by announcing that it has no intention of ratifying the treaty, an announcement that should be sent to the Treaty Depositary, which in the case of the CTBT is the secretary-general of the United Nations.

The U.S. has arguably already come within a whisker of unsigning the CTBT. In the 2018 Nuclear Posture Review, the U.S. stated that “the United States will not seek ratification of the Comprehensive Test Ban Treaty,” while simultaneously stating that it will continue to support the CTBT’s monitoring system and announcing that it will “not resume nuclear explosive testing unless necessary to ensure the safety and effectiveness of the U.S. nuclear arsenal, and [that it] calls on all states possessing nuclear weapons to declare or maintain a moratorium on nuclear testing.” The only thing left to do to make this statement a fully official unsigning is to send a letter restating that the U.S. will not proceed to ratification to the U.N. The administration should couple this with a request, paralleling its recent request on the Arms Trade Treaty, to the Senate to return the CTBT to the executive branch.

The point of unsigning the CTBT is not to return to U.S. nuclear testing . That is a decision that can be made only by policymakers acting on responsible and informed technical advice. But in a world where North Korea, Pakistan, and Iran continue to pursue or expand their nuclear weapons capabilities, and Russia continues to cheat, the U.S. should not foreclose its options. The CTBT was and remains a fundamentally flawed treaty. One important argument in favor of U.S. ratification has always been that if the U.S. ratifies the CTBT, dictatorships around the world will respect it. This argument from moral suasion is not supported by any evidence or by common sense, and has already proven a failure.

If the U.S. does proceed to a final unsigning of the CTBT, it should back up its suspicions about Russian cheating with as much information, and as comprehensive a case as possible, and it should make the basis of its concerns and the logic of its actions clear to its allies – especially the nuclear states of Great Britain and France. The serious allegations of Russian violations and the fundamental defects of the CTBT alike make a solid case for the U.S.’s decision not to ratify the treaty and justify completing this unsigning by a formal notification to the United Nations.