This is in stark contrast to what Biden said he would do as president. For most of his long political career Biden had fought to de-emphasize nuclear weapons, de-escalate nuclear tensions and embrace arms control. As far back as 1990 when he was a U.S. senator, Biden declared that “the military rationale for the first use of nuclear weapons has disappeared.” In 2020, while campaigning for the presidency, Biden sought to dramatically narrow the circumstances under which nuclear weapons could be used. In a Foreign Affairs article, he wrote that, “the sole purpose of the U.S. nuclear arsenal should be deterring and, if necessary, retaliating against a nuclear attack” — rather than to counter any conventional attack — and he pledged he would “work to put that belief into practice” as president. Even now Biden has stuck to his guns rhetorically, publicly condemning any hint that nuclear weapons should ever be used in a conventional war. In remarks at a fundraiser last month Biden declared that even the use of a tactical nuclear weapon in Ukraine would usher in “Armageddon” and said current tensions resembled the Cuban Missile Crisis.

And yet in practical terms, the administration has dropped those earlier pledges of de-escalation and reaffirmed the use of nuclear deterrence in conventional war. The “sole purpose” of America’s nuclear arsenal has now been expanded to shore up conventional deterrence, and what’s known as “no first use” seems to be off the table. As Biden’s 2022 Nuclear Posture Review concluded — echoing the last Nuclear Posture Review under Trump in 2018 — to make a pledge of “no first use” or a declaration of sole purpose at this time “would result in an unacceptable level of risk.” Indeed, Biden is expanding America’s “extended deterrence” nuclear posture into Asia, for example by pledging to deploy a nuclear-armed submarine in South Korea for the first time since the early 1980s. Last month, during military exercises, the U.S. landed a B-52 strategic bomber — a primary vehicle for nuclear bombs — in South Korea for the first time in three decades.

Why has Biden changed his approach? Several administration officials did not respond to a request for comment. But Biden’s new embrace of nuclear deterrence is clearly a response to dramatically changed circumstances. More than two years ago satellite photos stunned Washington’s national security community by revealing China’s dramatic — and highly secret — nuclear buildup, including as many as 300 new missile silos. Those revelations were followed by Putin’s invasion of Ukraine the following year and his repeated threats to deploy nuclear weapons, as well as Putin’s announcement earlier this year that Russia would be suspending its participation in New START, the last remaining U.S.-Russia arms control pact.

As a result, for the first time in its history, “the United States will need to deter two near-peer nuclear powers,” national security adviser Jake Sullivan said in a speech at the Arms Control Association in June, and thus “we’ve been laser-focused on modernizing the [NATO] alliance’s nuclear capabilities.” Sullivan was referring to an ongoing nuclear modernization program worth nearly $800 billion over 10 years to “ensure our deterrent capabilities remain secure and strong as we head into the 2030s,” as he put it. This includes the development of a new variant of the B61 gravity nuclear bomb, he said. Biden is also re-introducing a tactical nuclear deterrent to Europe by moving to certify the F-35A fighter as a so-called Dual Capable Aircraft (DCA) in order to carry that bomb.

The administration’s effort to beef up the U.S. nuclear arsenal comes at a moment when those two nuclear powers, China and Russia, are cooperating and sharing defense technology. Beyond that, U.S. conventional forces are stretched more thinly than ever, especially now with war erupting in the Middle East along with Europe, and with the Chinese military repeatedly forcing confrontations in the South China Sea. And that means an extended deterrence to protect U.S. allies in Asia and Europe is necessary to a degree that hasn’t been seen since the Cold War, some experts say.

Indeed, even before these latest revelations, Biden’s 2022 Nuclear Posture Review endorsed much of what the Trump administration had concluded four years before in its own NPR in 2018. Daryl Kimball, head of the Arms Control Association, said in a statement that the Biden administration merely “rubber stamps,” to a large extent, most of the Trump administration’s multibillion-dollar program for modernizing the U.S. nuclear arsenal, including 400 new land-based intercontinental ballistic missiles, a new fleet of nuclear-armed strategic submarines, a new strategic bomber (the B-21), a new air-launched cruise missile, a newly designed nuclear warhead (the W-93), and the refurbishment of other nuclear warhead types. To the alarm of some arms-control advocates, Biden’s Nuclear Posture Review also endorsed Trump’s initiative for the W76-2 lower-yield warhead on submarine-launched ballistic missiles.

The danger of introducing low-yield tactical weapons, which Russia has also done, is that it makes it easier to consider them part of a conventional war calculation — as Putin’s threats in Ukraine have shown. Kimball notes that in 2020, Biden had criticized the W76-2, saying it was a “bad idea” that makes the United States “more inclined” to use nuclear weapons. In a report published in early February, the Arms Control Association said other new technologies such as hypersonic missiles — which fly at five times the speed of sound and which Chinese scientists have taken the lead on — also could result in “blurring the distinction between a conventional and nuclear attack.”

The Biden administration insists that it is only modernizing, not expanding, America’s nuclear arsenal. “The United States does not need to increase our nuclear forces to outnumber the combined total of our competitors in order to successfully deter them,” Sullivan said in his speech. He also said the administration was eager to “to engage in new multilateral arms control efforts,” though he added: “We’re under no illusions that reaching risk reduction and arms control measures in that setting will be easy.”

On the contrary, all these developments have made a potentially escalating nuclear arms race all but inevitable with both China and Russia, some experts say. “We are in a new arms race, I don’t think there’s any doubt about it,” says Biden’s longtime former Senate expert on East Asia, Frank Jannuzi, who is currently CEO of the Maureen and Mike Mansfield Foundation, which seeks to promote peaceful U.S.-Asian relations.

“Biden believes in arms control,” adds Jannuzi. “He’d love to embrace a no-first use-policy and believe that nuclear arms are no longer needed. But the best military advice he’s getting is telling him that is not the case.”

All this means that, despite the positive noises coming out of San Francisco this week — where Biden is meeting Xi on the sidelines of the Asia Pacific Economic Cooperation summit — many nuclear experts see little immediate hope of any deal that might reverse this nuclear escalation.

Biden’s negotiations with Xi in San Francisco are expected to cover a wide range of issues, but U.S. officials say they want to focus on re-establishing military-to-military communication, which was suspended after then-Speaker Nancy Pelosi’s visit to Taiwan in 2022. The talks will also reportedly seek to develop protocols to prevent artificial intelligence from gaining too much influence in launch decisions or command and control. Experts are concerned that with rapidly evolving AI, decision-makers will come to depend far too much on AI strategic and tactical assessments. In a book published this year, AI and the Bomb, James Johnson of the University of Aberdeen warns of an accidental nuclear war precipitated by AI-driven intelligence on both the U.S. and Chinese sides, and “turbo-charged by AI-enabled bots, deepfakes, and false-flag operations.”

“For now, at least, there is a consensus amongst nuclear-armed powers that the devastating outcome of an accidental nuclear exchange obviates any potential benefits of automating the retaliatory launch of nuclear weapons,” Johnson said in an email.

Beyond that, however, huge gulfs remain, and many experts fear Washington and Beijing are headed into a tit-for-tat spiral of nuclear confrontation that could come to resemble the brinkmanship of the Cold War. According to an article this month in Foreign Affairs, “China’s Misunderstood Nuclear Expansion,” Beijing’s shift from its longtime policy of maintaining a small nuclear force of 220 weapons to a dramatic planned buildup of up to 1,000 operational warheads by 2030 (based on U.S. Defense Department estimates) is mainly a response to U.S. moves. Chinese officials fear that Washington is building up its nuclear forces to compensate for the fact that East Asia’s conventional military balance was shifting in China’s favor, the article said. Beijing also fears “that the United States has lowered its threshold for nuclear use — including allowing for limited first use in a Taiwan conflict — and that the U.S. military is acquiring new capabilities that could be used to destroy or significantly degrade China’s nuclear forces,” said the article’s authors, M. Taylor Fravel, Henrik Stålhane Hiim, and Magnus Langset Trøan.

Others agree with this assessment. “Locking the conflict at the conventional level is precisely what the U.S. does not want,” said Francesca Giovannini, executive director of the Project on Managing the Atom at the Harvard Kennedy School’s Belfer Center. The reason, she said, is the Pentagon fears that in “any Indo-Pacific confrontation between China and the U.S., the Chinese might gain the upper hand conventionally.”

That in turn has raised concerns that the U.S. and China will only talk past each other in any nuclear negotiation. The United States wants to “compartmentalize strategic stability from broader issues in the relationship,” as Sullivan put it in his June speech, or to put in guardrails to “de-conflict” the region. But China would likely only seek to discuss nuclear weapons in the context of the overall strategic relationship — including Washington’s military presence in East Asia and major concessions over Beijing’s right to reclaim Taiwan, according to Giovannini.

For U.S. military planners, the key challenge ahead is not so much to the traditional nuclear “triad,” the strategic arsenal based in planes such as the aging B-52 and new B-21, submarines, and land-based silos, says Brad Roberts, director of the Center for Global Security Research at Lawrence Livermore National Laboratory. Instead, he said, the U.S. military must scramble to compensate for decisions made in the early 1990s, when Washington brought home all of its forward-deployed nuclear tactical weapons in Asia and about 97 percent of those forward-deployed in Europe.

Into that vacuum Putin began developing tactical nukes before his Ukraine invasion, and China has developed some 900 dual-use missiles in the interim, suddenly putting the U.S. military on a backfoot. “We bet we could do extended deterrence from home, but our allies are telling us this isn’t adequate,” said Roberts, who served as policy director of the Obama administration’s Nuclear Posture Review in 2010. Adds Robert Soofer, who developed the 2018 Nuclear Posture Review as Trump’s deputy assistant secretary of defense for nuclear and missile defense policy, U.S. allies such as Japan and Korea want a more forward presence using submarines and other less vulnerable platforms.

“We can fly B-52 bombers with cruise missiles into the region from Guam,” says Soofer. “The problem is A, we don’t have them there now, and B, if you deploy the stuff, it’s vulnerable to a missile strike.”

As a consequence, urged on by several Armed Services committee members in both the Senate and House, some experts believe the administration may be reconsidering the one major Trump program it did eliminate, a new generation of nuclear-armed sea-launched cruise missiles. “They’re having an internal debate about how to respond not just to the developments in China’s posture but also the revelation that Putin may be less reliable and is capable of significant miscalculation,” said Roberts.

Yet another obstacle to significant nuclear negotiations is that neither China nor the U.S. has made clear what its strategic approach is. “We don’t know what China’s doctrine even is anymore as they embark on significant expansion of nuclear forces,” said Lynn Rusten of the Nuclear Threat Initiative. “At what point are they even going to acknowledge their nuclear force policies are changing?”

Some nuclear experts say an all-out arms race doesn’t have to happen. Henry Sokolski, head of the Nonproliferation Policy Education Center, said there are plenty of trade-offs possible, including an agreement by the U.S. to forswear any redeployment of U.S. nuclear weapons to South Korea and Japan, along with pressuring Tokyo and Seoul not to develop nukes, if the Chinese stop producing weapons-grade plutonium. “You need to say we are going to resist doing a quantitative race. The fix is to break the knot at the build-up point,” he said. “You need to be more honest with the Chinese and the public about how what they [Beijing] are doing is going to cause our allies to make demands that we don’t want to agree to.”

Another approach would be to threaten to redeploy the thousands of U.S. warheads taken off line in recent decades — the U.S. has 4,000 weapons in all, but only about 1,500 are now operable — unless Beijing agrees to a START-type treaty that would cover both its arsenal and Russia’s. Washington could also make the U.S. arsenal less vulnerable by shifting to submarines or creating more mobility in the ICBM force currently in silos rather than producing more weapons.

“You can either increase the size of our arsenal, or make it more survivable, or some combination of the two,” says Soofer.

Jannuzi said that, during its first two and a half years, the Biden administration took the proper approach to the China threat by shoring up its alliances and talking tough to Beijing, often in public forums. The problem, he said, is that “they have not done much yet on task No. 2, which is negotiating with China to make sure the world’s two largest economies are not at knife point. That job remains undone.”