In early February 2026, US Under Secretary of State Thomas DiNanno claimed China conducted a nuclear test on 22 June 2020 and used 'decoupling' to reduce detectability. The CTBTO – the treaty organisation that runs the global nuclear test monitoring system – publicly rejected the claim, saying its network detected no event consistent with a nuclear weapon test at that time. 

This is not just a technical spat. It lands days after the expiry of New START, the last major US–Russia treaty that constrained deployed strategic arsenals. With the last big limits gone, words and signals matter more. Public allegations can shape perceptions of who is breaking the rules, who is falling behind, and who should be pulled into the next negotiating framework. 

So the key question is not just whether China tested in 2020, but what Washington gains by making the allegation now – and what it signals about the next phase of arms control and nuclear modernisation. 

What the test-ban treaty does, and why low-yield ambiguity matters 

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) prohibits any nuclear weapon test explosion or any other nuclear explosion. The United States and China have signed but not ratified it. As signatories, both are widely understood to carry a duty under Article 18 of the Vienna Convention not to undermine the treaty’s object and purpose while ratification remains pending.

States can label some activities 'experiments' rather than 'tests', and disputes over definitions can become disputes over intent

The political problem is that 'zero-yield' and 'very low yield' can blur at the margins. States can label some activities 'experiments' rather than 'tests', and disputes over definitions can become disputes over intent. That makes treaty politics vulnerable to a familiar dynamic: when verification is contested, accusations become a tool of leverage. 

The CTBT’s credibility depends on separating technical judgement from political signalling. When allegations are made in a highly politicised moment, they risk pulling the monitoring system into great-power bargaining, regardless of whether the underlying claim is true. 

Verification: what decoupling can and cannot do 

'Decoupling' means attempts to reduce the seismic signal of an underground blast. You might do this, for example, by detonating inside a cavity. In theory, this can complicate monitoring. In practice, large concealment effects are hard to achieve. They require specific geology, major engineering, and scale. 

That is why the CTBTO’s response matters. The organisation runs the International Monitoring System and routinely analyses signals that could indicate nuclear explosions. In this case, the CTBTO said that it detected no event consistent with a nuclear test at the time and place alleged. 

The point is not the physics but the politics. If Washington alleges hidden testing and the monitoring body disputes it, the dispute itself becomes strategic. It can harden bargaining positions, increase demands for transparency, and strengthen calls to bring China into a new framework. It also creates space for the United States to argue it needs 'options' of its own. Uncertainty, in short, can become a political weapon.

In theory, you can reduce the seismic signal of a nuclear blast – by detonating inside a cavity, for example. In practice, such concealment is hard to achieve

Of the two readings, diplomatic leverage seems more immediate; domestic normalisation more dangerous. If the goal is to pull Beijing into talks, expect renewed calls for trilateral negotiations, transparency demands, and allied coordination. If the aim is to prepare the ground for US testing, watch for rhetoric about restoring 'test readiness', funding or infrastructure moves at the Nevada site, and framing that portrays restraint as one-sided. The direction of travel matters more than the disputed event itself. 

Two strategic uses of the Chinese nuclear testing allegation 

Washington has long argued that any post-New START arrangement must include China. Beijing has resisted, citing its smaller arsenal and insisting that other nuclear powers also matter. A public allegation of Chinese testing strengthens the US claim that China must be inside the tent. It also reframes the issue from 'strategic balance' to 'rules and restraint', which plays well in diplomacy. 

The allegation also supports a second, more domestic logic: preparing the ground to justify US testing as a response to others. After New START’s expiry, arguments for 'modernisation', 'hedging', and 'deterrence' can expand quickly. In that environment, claims of Chinese testing – even contested ones – can be used to argue that restraint is unilateral and therefore unsustainable. 

These logics can coexist. A credible threat to resume testing can be used as leverage to pull others into negotiations. At the same time, talk of leverage can be used to make resuming testing appear reasonable. The risk is a spiral in which bargaining and modernisation reinforce each other, and the political threshold against testing erodes. 

What would genuinely strengthen restraint 

If the aim is to deter testing and stabilise nuclear politics after New START, the most effective steps are institutional, not rhetorical. 

Washington and Beijing can clarify their positions on 'zero-yield' practices and expand transparency around subcritical experiments – experiments that do not produce a nuclear blast – and related safety activities. Clearer definitions reduce room for political manipulation.

If leaders argue that hidden testing poses a serious threat, they should be prepared to strengthen the legal and institutional machinery that makes cheating harder to conceal

The CTBTO’s authority also depends on protecting technical assessment from political pressure. Public accusations should be accompanied by evidence and a willingness to accept independent scrutiny. 

Ratification of the CTBT remains politically difficult in both countries. Yet the logic is simple: if leaders argue that hidden testing poses a serious threat, they should be prepared to strengthen the legal and institutional machinery that makes cheating harder to conceal and easier to expose. 

The world after 5 February 2026 will reward clarity over insinuation. If allegations of secret tests become a routine instrument of rivalry, the outcome will not be stronger arms control. It will be a lower threshold for renewed testing and a shorter path to an uncontrolled three-way arms race.

☢️ No.34 in a series on the Nuclear Politics Paradox

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