When US President Barack Obama signed the latest arms-control treaty with Russia in April 2010, he called it “an important first step”. But the administration has been tripped up by Republican opposition to the New Strategic Arms Reduction Treaty (New START), which would reduce both nations' arsenals by roughly one-third. The Republicans are blocking the treaty with pseudoscientific arguments about the state of the country's weapons complex. Yet it is politics, not science, that is behind their move.

Earlier this week, Arizona senator Jon Kyl, the number-two Republican in the Senate, said he believed that the treaty could not be ratified by the end of the year. Debate over its merits would take “at least two weeks”, and Senate Democrats had not provisioned enough time for the discussion, Kyl said on US network NBC's Meet the Press talk show.

Pushing a vote on the treaty into 2011 would present it to a new Senate — containing more Republicans — potentially making it less likely to pass. Such a delay would also increase the chances of Kyl, no fan of arms control, giving the Obama administration a bloody nose.

The debate Kyl hungers for is less about the treaty itself than it is about the state of the US nuclear complex. In a 24 November memo to Senate Republicans, Kyl and Bob Corker (Republican, Tennessee) characterized nuclear-weapons scientists as mechanics working in a decrepit garage on a fleet of 30-year-old Ferraris. The scientists are “responsible for assuring that, at any given moment, each of the eight finely tuned cars will respond to the key turn”, they wrote.

Implicit in this analogy is that there is some uncertainty over how the country's decades-old nuclear weapons will behave if they are ever used. Moreover, Kyl implies that weapons scientists are ill-equipped to analyse and diagnose problems associated with the arsenal.

There is little in the open scientific literature to support these positions. The chief concern surrounding ageing nuclear weapons has been that their plutonium triggers will be damaged by self-irradiation. Yet a 2006 review of weapons-lab data by the independent JASON scientific advisory group found that the triggers are heartier than expected and will last for at least 85 years.

Similarly, the image of a rickety garage is hardly appropriate. Weapons scientists have a slew of modern tools to ensure that their weapons continue to work effectively. Last year saw the start-up of the US$3.5-billion National Ignition Facility, a giant laser at Lawrence Livermore National Laboratory in California that aims to replicate the forces inside an exploding warhead. Livermore's sister lab, Los Alamos National Laboratory in New Mexico, is home to a radiographic facility that can create three-dimensional X-rays of dummy bombs as they explode. And scattered across the weapons complex are powerful supercomputers that can simulate full nuclear explosions based on data from these experiments and from past tests.

The weapons labs want more, and have found an ally in Kyl. Over the summer, the senator conducted tours of the labs, and came away with strengthened demands for funds, including money for modern uranium and plutonium manufacturing facilities. Many of the arguments he uses have been used by some within the weapons complex for years to call for a return to underground testing, as well as the development of new kinds of 'reliable' weapons.

The Obama administration had offered Kyl a decade-long funding commitment worth more than $85 billion to the weapons complex in exchange for agreement on the treaty, but the senator has continued to advance his flimsy political arguments over the fitness of the country's complex. As Nature went to press, Obama was due to host a bipartisan meeting to try to resolve the dispute.

There is certainly a need to debate the future shape and size of the US weapons complex, but there is no need to do so before ratifying New START. The facts speak for themselves: the weapons will work, and the scientists watching them have the tools to make sure that they do.