The last remaining nuclear arms pact between Russia and the United States is set to expire Thursday, removing any caps on the two largest atomic arsenals for the first time in more than a half-century.

The termination of the New START Treaty would set the stage for what many fear could be an unconstrained nuclear arms race.

Russian President Vladimir Putin declared readiness to stick to the treaty’s limits for another year if Washington follows suit, but President Donald Trump has been noncommittal about extending it.

Trump has repeatedly indicated he would like to keep limits on nuclear weapons and involve China in arms control talks, a White House official who was not authorized to talk publicly and spoke on condition of anonymity said Monday. Trump will make a decision on nuclear arms control “on his own timeline,” the official said.

Beijing has balked at any restrictions on its smaller but growing nuclear arsenal.

Kremlin spokesman Dmitry Peskov said Tuesday it would be a “more dangerous” world without limits on U.S. and Russian nuclear stockpiles.

Arms control advocates long have voiced concern about the expiration of New START, warning it could lead to a new Russia-U.S. arms race, foment global instability and increase the risk of nuclear conflict.

Failure to agree on keeping the pact’s limits will likely encourage a bigger deployment, said Daryl Kimball, executive director of the Arms Control Association in Washington.

“We’re at the point now where the two sides could, with the expiration of this treaty, for the first time in about 35 years, increase the number of nuclear weapons that are deployed on each side,” Kimball told The Associated Press. “And this would open up the possibility of an unconstrained, dangerous three-way arms race, not just between the U.S. and Russia, but also involving China, which is also increasing its smaller but still deadly nuclear arsenal.”

Kingston Reif of the RAND Corporation, a former U.S. deputy assistant secretary of defense, also warned during an online discussion that “in the absence of the predictability of the treaty, each side could be incentivized to plan for the worst or to increase their deployed arsenals to show toughness and resolve, or to search for negotiating leverage.”

Putin repeatedly has brandished Russia’s nuclear might since sending troops into Ukraine in February 2022, warning Moscow was prepared to use “all means” to protect its security interests. In 2024, he signed a revised nuclear doctrine lowering the threshold for nuclear weapons use.

Signed in 2010

New START, signed in 2010 by U.S. President Barack Obama and his Russian counterpart, Dmitry Medvedev, restricted each side to no more than 1,550 nuclear warheads on no more than 700 missiles and bombers — deployed and ready for use. It was originally supposed to expire in 2021 but was extended for five more years.

The pact envisioned sweeping on-site inspections to verify compliance, although they stopped in 2020 because of the COVID-19 pandemic and never resumed.

In February 2023, Putin suspended Moscow’s participation, saying Russia couldn’t allow U.S. inspections of its nuclear sites at a time when Washington and its NATO allies have openly declared Moscow’s defeat in Ukraine as their goal. At the same time, the Kremlin emphasized it wasn’t withdrawing from the pact altogether, pledging to respect its caps on nuclear weapons.

In offering in September to abide by New START’s limits for a year to buy time for both sides to negotiate a successor agreement, Putin said the pact's expiration would be destabilizing and could fuel nuclear proliferation.

Rose Gottemoeller, the chief U.S. negotiator for pact and a former NATO deputy secretary-general, said extending it would have served U.S. interests. “A one-year extension of New START limits would not prejudice any of the vital steps that the United States is taking to respond to the Chinese nuclear buildup,” she told an online discussion last month.

Previous pacts

New START followed a long succession of U.S.-Russian nuclear arms reduction pacts, starting with SALT I in 1972 signed by U.S. President Richard Nixon and Soviet leader Leonid Brezhnev — the first attempt to limit their arsenals.

The 1972 Anti-Ballistic Missile Treaty restricted the countries’ missile defense systems until President George W. Bush took the U.S. out of the pact in 2001 despite Moscow’s warnings. The Kremlin has described Washington’s efforts to build a missile shield as a major threat, arguing it would erode Russia’s nuclear deterrent by giving the U.S. the capability to shoot down its intercontinental ballistic missiles.

As a response to the U.S. missile shield, Putin ordered the development of the Burevestnik nuclear-tipped and nuclear-powered cruise missile and the Poseidon nuclear-armed and nuclear-powered underwater drone. Russia said last year it successfully tested the Poseidon and the Burevestnik and was preparing their deployment.

Also terminated in 2019 was the Intermediate-range Nuclear Forces Treaty, which was signed in 1987 and banned land-based missiles with a range between 500-5,500 kilometers (310-3,400 miles). Those missiles were seen as particularly destabilizing because of their short flight time to their targets, leaving only minutes to decide on a retaliatory strike and increasing the threat of a nuclear war on a false warning.

In November 2024 and again last month, Russia attacked Ukraine with a conventional version of its new Oreshnik intermediate-range ballistic missile. Moscow says it has a range of up to 5,000 kilometers (3,100 miles), capable of reaching any European target, with either nuclear or conventional warheads.

Trump's ‘Golden Dome’

Without agreements limiting nuclear arsenals, Russia “will promptly and firmly fend off any new threats to our security,” said Medvedev, who had signed the New START treaty and is now deputy head of Putin's Security Council.

“If we are not heard, we act proportionately seeking to restore parity,” he said in recent remarks.

Medvedev specifically mentioned Trump's proposed Golden Dome missile defense system among potentially destabilizing moves, emphasizing a close link between offensive and defensive strategic weapons.

Trump’s plan has worried Russia and China, Kimball said.

“They’re likely going to respond to Golden Dome by building up the number of offensive weapons they have to overwhelm the system and make sure that they have the potential to retaliate with nuclear weapons,” he said, adding that offensive capabilities can be built faster and cheaper than defensive ones.

Trump’s October statement about U.S. intentions to resume nuclear tests for the first time since 1992 also troubled the Kremlin, which last conducted a test in 1990 when the USSR still existed. Putin said Russia will respond in kind if the U.S. resumes tests, which are banned by a global treaty that Moscow and Washington signed.

U.S. Energy Secretary Chris Wright said in November that such tests would not include nuclear explosions.

Kimball said a U.S. resumption of tests “would blow a massive hole in the global system to reduce nuclear risk,” prompting Russia to respond in kind and tempting others, including China and India, to follow suit.

The world was heading toward accelerated strategic competition, he said, with more spending and increasingly unstable relations involving the U.S., Russia, and China on nuclear matters.

“This marks a potential turning point into a much more dangerous period of global nuclear competition, the likes of which we’ve not seen in our lifetimes,” Kimball added.

Associated Press writer Michelle L. Price in Washington contributed.

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The last US-Russian nuclear pact is about to expire, ending a half-century of arms control

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