The expiration of the last remaining nuclear treaty between the United States and Russia on Thursday has sparked fears about a nuclear arms race, with the two biggest nuclear superpowers without limits on their arsenals for the first time in decades.

“The worst case is it spirals and then some unforeseen or foreseeable incident touches off a conflict that escalates rapidly to a nuclear conflict,” said Thomas Countryman, a former acting undersecretary of state for arms control and international security.

Though some experts argue the limitations of the New START treaty were outdated and unnecessarily constrained the US, especially when China is looking to expand its nuclear arsenal.

The landmark treaty went into force in February 2011. It capped both countries at 1,550 deployed nuclear warheads; 700 deployed intercontinental ballistic missiles, submarine-launched ballistic missiles and heavy bombers equipped to transport nuclear weapons; and 800 “deployed and non-deployed” launchers. It put limits on Russian intercontinental nuclear weapons that could reach the US.

But critics of the treaty, including President Donald Trump, pointed out it did not cover China, which is rapidly expanding its nuclear arsenal and could have some 1,500 nuclear warheads by 2035 if they continue to expand their stockpile at the current pace, according to a Pentagon report from 2022.

The treaty was originally in place for 10 years. In 2021, the US and Russia agreed to extend it for another five years, through February 4, 2026.

The agreement was not eligible to be extended again, but the two countries could agree to continue to adhere to the caps outlined in the treaty. Concerns over the future of arms control – which the US and Russia have worked on together for decades – comes as Trump also vowed last year that the US would resume nuclear testing, but there has been no movement towards that end.

Last September, Russian President Vladimir Putin proposed doing so for another year. At the time, Trump said the proposal “sounds like a good idea to me.”

However, Trump in recent weeks has expressed little concern about the lapse, telling the New York Times, “If it expires, it expires. We’ll do a better agreement.”

And on Wednesday, Secretary of State Marco Rubio suggested that the US would not agree to maintain the limits of the treaty, citing Trump’s call for a nuclear deal between the US, Russia and China.

“The president has been clear in the past that in order to have true arms control in the 21st century, it’s impossible to do something that doesn’t include China because of their vast and rapidly growing stockpile,” he said.

Beijing has consistently rebuffed the idea of trilateral negotiations both privately and publicly.

Russia’s Foreign Ministry on Wednesday said they had received no answer from the Trump administration and that public comments from the US government indicate “that our ideas have been deliberately left unanswered.”

“This approach seems erroneous and regrettable,” the statement said.

The foreign ministry said that “in the current circumstances,” they assume the two countries “are no longer bound by any obligations or symmetrical declarations in the context of the Treaty, including its core provisions, and are in principle free to choose their next steps.”

Asked about the statement, a Trump administration official told CNN, “President Trump has spoken repeatedly of addressing the threat nuclear weapons pose to the world and indicated that he would like to keep limits on nuclear weapons and involve China in arms control talks.”

“The president will decide the path forward on nuclear arms control, which he will clarify on his own timeline,” the official said.

“We do not benefit from a wasteful, inefficient arms race. We do not benefit from a lack of predictability and transparency in knowing what the Russian nuclear program is up to. We don’t benefit from potential miscommunication or miscalculation based on a lack of information,” said Paul Dean, a former assistant secretary of state for arms control, deterrence, and stability.

How the Trump administration responds to the treaty’s expiration is yet to be determined, though former officials and experts said the US may upload more nuclear warheads, reversing moves it took to pare back its posture to comply with the treaty when it was introduced.

Some experts suggest such action is needed to reassure allies who might be tempted to build their own nuclear arsenals.

“If people are worried about Russia and China building up, they should have been worried a decade ago when they were already building up their nuclear arsenals and the US was showing restraint,” said Heather Williams, a director on nuclear issues at CSIS. “If we don’t show nuclear resolve our allies will wonder will the US come to our aid, do we have to develop our own nuclear programs.”

But rapid action by Russia is also likely if the US makes moves to expand beyond the treaty’s limits.

Rose Gottemoeller, who served as chief US negotiator for New START, said she believes the worst-case scenario is a rapid campaign carried out by Russia to upload additional nuclear warheads “that essentially leaves us in the dust while we’re still trying to get organized and the Chinese are building up steadily again.”

She told CNN that the US could benefit from a year’s extension to the limits because the country is “not immediately ready to rush into anything.”

“We’ve got work to do, to plan and prepare,” she said, noting that it would take time to undo the changes made to submarines and bombers in order to adhere to the treaty.

Russia, she said, is much better prepared to start uploading their missiles quickly.

“They have active warhead production lines as well as active production lines for other related components for their missile systems that they would be able to upload rapidly,” Gottemoeller said. “We know they have that industrial capacity available, and we do not have it.”

Gottemoeller also noted that a one-year extension could be an “easy” diplomatic win for Trump. She also said the extension of the limits “really gives us a chance to prepare right for what we need to do against the Chinese.”

But others disagree about the benefits of pursuing an extension of the existing limits.

Matthew Kroenig, vice president and senior director of the Atlantic Council’s Scowcroft Center for Strategy and Security, told CNN that he does not believe adhering to the limits is in the US interest.

“In theory, it is nice to have limitations, but the main goal of US nuclear weapons is to deter nuclear war, not to have treaties,” he said.

He said China is not in the same position that it was when New START was negotiated and the existing limits are not enough to deter both Moscow and Beijing.

“China is a near-peer superpower or will be a nuclear superpower, and so now we need a strategy to deter nuclear war with Russia and China, with China’s much larger force,” he told CNN.

He pointed to the October 2023 findings of a bipartisan strategic posture commission, on which both he and Gottemoeller served, that said the “size and composition of the nuclear force must account for the possibility of combined aggression from Russia and China.”

“U.S. strategy should no longer treat China’s nuclear forces as a ‘lesser included’ threat,” it said.

“Biden administration officials have publicly said now that they took the recommendation seriously and took all the necessary steps to prepare for an upload of additional warheads. So they didn’t actually do it, but they said that they’ve done everything that if the Trump administration decided to go in that direction, the department would be prepared,” Kroenig said.

Trump pursued a trilateral arms control agreement between the US, Russia and China during his first term, and Trump administration officials have consistently made efforts to engage China on the topic throughout the last year, according to a senior administration official. But China has consistently refused to engage in talks that could limit their growing nuclear arsenal.

Multiple track-two discussions on strategic stability between the US and China have occurred over the last year, sources familiar with the discussions said. One former official involved in those talks told CNN that China appears more open to the overall discussion, even if they refuse to broach the topic of limitations on their arsenal.

“This may be due to growing awareness that the size of their nuclear arsenal and forthcoming collapse of all structured arms control agreement between US and Russia have cast them into a world less familiar to them,” the former official said.

Still, without a clear understanding on what will bring China to the table for serious dialogue on the topic, abandoning New START and the pursuit of interim agreement is a risky move, some experts said.

“We could see a dangerous three-way arms race” between Russia, the US and China said Daryl Kimball, the executive director of the Arms Control Association, “but all of that could be avoided or mitigated with some simple common sense, diplomatic efforts.”

Although “the expiration of New START is not the first setback in global risk reduction efforts,” Kimball said, its occurrence “in the midst of the Trump administration’s kind of wrecking ball approach to international rules and treaties could be the starting point for a new kind of US-Russian and US-Chinese, unbridled, unconstrained arms race that is costly for all countries.” (CNN)

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