Since Russia invaded Ukraine in 2022, President Vladimir Putin and other Kremlin voices have frequently threatened the West with its nuclear arsenal.
On the first day of the war, Putin said "whoever tries to impede us, let alone create threats for our country and its people, must know that the Russian response will be immediate and lead to consequences you have never seen in history."
Over nearly 2-1/2 years of fighting, the West has given Ukraine billions of dollars of advanced weapons, some of which have struck Russian soil. And while there have been more Kremlin threats — and even the deployment of battlefield nuclear weapons in Belarus, just over the border from Ukraine — so far it has remained only a blunt message.
What could finally trigger a nuclear response?
Asked that in June by international news agencies, Putin pointed to Russia's so-called nuclear doctrine.
"Look what is written there," he said at the St. Petersburg session. "If somebody's actions threaten our sovereignty and territorial integrity, we consider it possible to use all means at our disposal."
Now Russian hawks are urging him to change the doctrine to lower the threshold for using nuclear weapons, and Putin says the document could be modified to take into account the evolving global situation.
What is Russia's nuclear doctrine?
Formally known as the "Basic Principles of State Policy on Nuclear Deterrence," it was signed by Putin in 2020 and outlines when Russia could dip into its atomic arsenal, the world's largest.
It describes nuclear weapons as "a means of deterrence," noting that their use is an "extreme and compelled measure." It declares that Russia "takes all necessary efforts to reduce the nuclear threat and prevent aggravation of interstate relations that could trigger military conflicts, including nuclear ones."
The document states that "nuclear deterrence is aimed to provide comprehension by a potential adversary of the inevitability of retaliation in the event of aggression against the Russian Federation and/or its allies."
What does it say will trigger using nuclear weapons?
Russia could use them, the doctrine says, "in response to the use of nuclear and other types of weapons of mass destruction against it and/or its allies, as well as in the event of aggression against the Russian Federation with the use of conventional weapons when the very existence of the state is in jeopardy."
It says nuclear weapons could be used under the following specific situations:
— If reliable information is received about the launch of ballistic missiles targeting the territory of Russia or its allies.
— If nuclear weapons or other weapons of mass destruction are used against Russia or its allies.
— If an enemy attack with conventional weapons threatens Russia's existence.
— If there are attacks on critically important Russian government or military facilities that could undermine the country's retaliatory nuclear strike capability.
Has any attack so far come close to crossing this threshold?
As Russia attacked parts of northeastern Ukraine near the city of Kharkiv, Washington has allowed Kyiv to use longer-range U.S.-supplied weapons for strikes in Russian territory in the border region. But these attacks have been limited in scope and would not seem to pose an existential threat that would fall under the nuclear doctrine.
However, the hawks in Moscow have pointed to a series of Ukrainian attacks on Russian air bases that host long-range nuclear-capable bombers earlier in the conflict, as well as recent raids on early-warning radars.
They say these circumstances would seem to warrant the use of nuclear weapons as laid out in the doctrine.
Russian officials haven't commented on the attacks on the more sensitive targets. The early-warning radars are designed to spot the launch of U.S. missiles to allow Russia to launch its own nuclear-tipped missiles before they are destroyed.
James Acton, co-director of the nuclear policy program at the Carnegie Endowment, said in a recent commentary that Ukrainian attacks on the early-warning radars could prompt the Kremlin to think Washington had encouraged such strikes to try to weaken Russia's nuclear deterrent.
"If Moscow believes that Washington could conduct a successful preemptive attack on its nuclear forces, its trigger finger could get very itchy, raising the risk that Russia might launch a large-scale nuclear attack based on a false or misinterpreted warning," Acton said.
What changes in the doctrine are under discussion?
The Kremlin's nuclear threats have been dialed down recently amid Moscow's battlefield successes in Ukraine. However, there also have been calls in Russia for changing the nuclear doctrine, and Putin said it could be modified, depending on global events.
Hawks have called repeatedly for sharpening it, arguing the current document is too weak and vague. They say the doctrine hasn't deterred the West from increasing aid to Ukraine and gives the impression that Moscow won't ever resort to nuclear weapons.
Foreign affairs expert Dmitri Trenin, of the Institute of World Economy and International Relations, a state-funded Moscow think tank, suggests revising it to declare that Russia could strike first with nuclear weapons when "the core national interests are at stake," like in Ukraine.
"The acute task in the third year of military confrontation is to prevent NATO's deeper engagement in it," Trenin wrote recently. "If we don't do it, the inertia of persistent escalation by the West will lead to a direct clash between Russian and NATO militaries, which is fraught with a global nuclear war."
At the international forum in St. Petersburg, Sergei Karaganov, a foreign policy expert who advises the Kremlin, also urged Putin to amend the doctrine to lower the threshold for the use of nuclear weapons.
"I hope it will be changed soon to give you the formal right to respond to any strikes on our territory with a nuclear strike," he told the Russian leader. "I hope that such a provision will be added to our doctrine to help cool our adversaries."
Karaganov likened the West to Sodom and Gomorrah, the biblical cities destroyed by God with a rain of fire for their wickedness. "Let's remember that rain and try to make humankind come to its senses," he said.
Putin responded cautiously, saying that he currently sees no threats that would warrant nuclear weapons use, but he also held the door open to revising the policy.
"This doctrine is a living instrument, we are carefully watching what's going on in the world around us, and we don't exclude making changes in the doctrine," he said.
The need to modify the document, he said, was driven by concerns about the West pondering the possible deployment of low-yield nuclear weapons. Putin didn't give specifics, but his comments could refer to U.S. discussions on deploying low-power submarine-launched nuclear missiles.
Proponents say such weapons are needed to counter Russian threats, while critics argue they could lower the threshold for the U.S. using nuclear weapons and increase the risk of war.
"Nuclear devices of extremely low power are being developed, and we are aware of the ideas circulating in expert circles in the West that such strike assets could be used, and there is nothing particularly horrible about it," Putin said. "We are obliged to take notice of that, and we are taking notice."
