Fears of Russian Nuclear Weapons Use Have Diminished, but Could Re-emerge

WASHINGTON — Last fall, tensions in Washington reached a crescendo as Moscow made persistent nuclear threats and U.S. intelligence reported discussions among Russian military leaders about the use of such weapons.

Concerns remain over Russia using a nuclear weapon, but the tensions have since abated. Several factors explain why, officials said: A more stable battlefield, China’s warnings against the use of nuclear weapons, improved communications between Moscow and Washington and an increased role of the International Atomic Energy Agency in Ukraine have contributed to a measure of stability.

President Vladimir V. Putin of Russia, a senior U.S. official said recently, may well have come to the conclusion that the threats, which he once saw as leverage, were backfiring.

The possibility of nuclear escalation continues to influence American decisions over what advanced weaponry to give Ukraine. But nearly a year into the war there, American policymakers and intelligence analysts have more confidence that they understand at least some of Mr. Putin’s red lines — and what kinds of support for Ukraine will prompt statements of condemnation versus what might risk something more dangerous.

Inside the Biden administration, officials caution that Russia’s threats over nuclear escalation are not over, and that the next time the Kremlin wants to remind the West about the power of its arsenal, it could potentially move a nuclear weapon that it knows can be observed by the United States. The U.S. officials spoke on the condition of anonymity to discuss deliberations.

The Pentagon continues to war game what might happen if Mr. Putin moves tactical weapons into position as a reminder that he can back up his conventional forces. But overwrought threats, in the absence of other intelligence, are causing little stir. A nuclear threat last month by Dmitri Medvedev, the former Russian president who serves as a deputy chairman of Russia’s security council, was met mostly with shrugs in the United States.

This week, in response to Germany’s decision to supply Ukraine with tanks, Mr. Putin delivered a veiled warning. “We aren’t sending our tanks to their borders,” he said. “But we have the means to respond, and it won’t end with the use of armor. Everyone must understand this.”

At a speech in Washington on Thursday, William J. Burns, the C.I.A. director, said the United States had to take seriously the nuclear “saber rattling” of Mr. Putin and his advisers. Mr. Burns added that he had to made clear to Russian officials the serious consequences of any use of tactical nuclear weapons in Ukraine.

“It is a risk we cannot afford to take lightly; on the other hand, the purpose of the saber rattling is to intimidate us, as well as our European allies and the Ukrainians themselves,” he said. “So I think we have to stay on an even keel in weighing those threats carefully but also not being intimidated by them.”

Heightened nuclear fears in October came against the backdrop of a successful counteroffensive by the Ukrainian military when it reclaimed a huge swath of territory east of Kharkiv, in the northeast. It then made a drive at Kherson, in the south, forcing the Russian military to eventually retreat from there. With their army in disarray, Mr. Putin and other Russian officials warned against Ukraine’s use of a so-called dirty bomb: a crude device that spreads radiological material but does not create a nuclear reaction. U.S. officials were unsure what Moscow might do.

As winter set in and Russia managed to pull its forces from Kherson in a relatively orderly retreat, the battlefield stabilized. Intense fighting remains around Bakhmut, in the Donbas region, but there are no drastic territorial shifts. In the south, the Russians have dug in, intensifying their defenses; they do not appear to be on the brink of a collapse that could make their leaders think that only the use of a tactical nuclear weapon could stave off defeat.

U.S. officials also credit an improved dialogue with Moscow, at least over nuclear issues.

Amid Russia’s battlefield failures, U.S. intelligence concluded that Russian military officials had discussed situations in which a tactical nuclear weapon could be used. Two calls between Defense Secretary Lloyd J. Austin III and the Russian defense minister, Sergei K. Shoigu, worried Washington because Mr. Shoigu had raised concerns about Ukraine’s possible use of a dirty bomb.

The claims were propaganda, but some U.S. officials said Russian officials appeared to believe their own disinformation. Getting International Atomic Energy Agency inspectors into Ukraine — and, in early November, when the agency found no evidence of a dirty bomb — helped ease tensions.

A call in late October between Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, and his counterpart, Gen. Valery V. Gerasimov, Russia’s chief of the general staff, also relieved tensions. In the call, according to two U.S. officials, General Gerasimov outlined a use of nuclear weapons consistent with Washington’s understanding of Russia’s nuclear doctrine.

Mr. Burns also met with his counterpart, Sergei Naryshkin, the director of Russia’s foreign intelligence service, in Turkey to warn Russia about its nuclear threats. The purpose of the trip, Mr. Burns said on Thursday, was “to make very clear the serious consequences of any use of tactical nuclear weapons.” The meeting, officials said, opened up a new line of communication with Russian leadership.

President Biden has been criticized for being overly cautious in sending assistance to Ukraine, but U.S. officials insist his top priority is ensuring that the war does not escalate into a nuclear conflict between Russia and the West. And while American officials have a better sense of what actions will prompt Russian reaction, determining what might provoke Mr. Putin is imperfect.

“This is a very dynamic situation,” Senator Jack Reed, Democrat of Rhode Island and the chairman of the Armed Services Committee, said after a visit to Kyiv last month. “It’s a day-to-day basis on what’s a red line.”

Administration officials say they are trying to distinguish between Mr. Putin’s threats and his actual opportunities to use nuclear weapons, in hopes of cutting those off.

So far, they have no evidence that he is moving nuclear weapons toward the battlefield, though they note that with some of his tactical weapons — small battlefield arms, including some that can fit into an artillery shell — they might not see such movement. But the officials expect that if Mr. Putin wants to raise the level of alarm, he will make a public show of transferring weapons or make sure Western allies pick up chatter among the units that control those weapons.

“We don’t have any indication that Mr. Putin has any intention to use weapons of mass destruction — let alone nuclear weapons, tactical or otherwise,” John Kirby, a White House spokesman, said at a news briefing last week. “We monitor as best we can, and we believe that — that our strategic deterrent posture is appropriate. But we have seen no indication that that’s in the offing.”

U.S. officials have repeatedly said publicly that Russia might use a nuclear weapon if Mr. Putin’s grip on power was threatened, if Moscow thought NATO would directly enter the war in Ukraine, or the Russian army faced a sudden, catastrophic defeat.

Throughout the war in Ukraine, U.S. officials have developed a more refined, though imperfect, sense of what actions might escalate the conflict. Weapons sent to the country — even those with increasingly advanced abilities — have so far not provoked a response from Russia, given that Ukraine has been using them within its borders.

But the ever-changing battlefield dynamics could shift the Russian calculus on the use of nuclear weapons.

Still, their use makes little sense for Russia, U.S. officials insist — not least because it could potentially alienate countries that have either explicitly supported Russia or remained neutral.

The United States and its allies say that appealing to Russia’s partners is vital to warning Moscow against a nuclear weapon. China’s leader, Xi Jinping, whose support Mr. Putin needs, issued an explicit warning — pushed in part by Chancellor Olaf Scholz of Germany during his visit to Beijing in November. The German diplomatic push came with the support of the United States, several U.S. officials said.

Mr. Scholz said publicly that his joint statement with Mr. Xi on the use of nuclear weapons justified his visit to Beijing.

“Because the Chinese government, the president and I were able to declare that no nuclear weapons should be used in this war,” Mr. Scholz said, “that alone made the whole trip worthwhile.”

Eric Schmitt contributed reporting.