Russian leader Vladimir Putin has raised the specter of using a nuclear weapon in his war with Ukraine. Putin has done this before, though he was more explicit in a speech last Friday, and he says he's not bluffing.
The U.S., he said, set a "precedent" when it dropped two atomic bombs on Japan in 1945 at the end of World War II. So what is the likelihood that the Russian leader might use of such weapons?
"We have a 77-year tradition, some call it a taboo, of non-use of nuclear weapons. Russia is threatening that," said Matthew Bunn a professor at the Harvard Kennedy School. He's spent his career studying nuclear weapons, including a stint in the 1990s as a White House adviser when President Bill Clinton was in office. "We need to do everything we can to maintain that tradition of not using nuclear weapons in combat."
Here are a number of key questions surrounding Russia possible use of nuclear weapons.
Q. Why is Vladimir Putin raising the possibility of a nuclear attack now?
Ukraine's military keeps regaining ground in the east and the south of the country, which Russia had seized earlier in the war. With these battlefield setbacks, Putin is facing pressure from the pro-war camp in Russia. Many of these hardliners say Russia needs to unleash the full force of its military in Ukraine.
This has likely contributed to Putin's recent escalation, which includes the mobilization of 300,000 additional troops, annexing Ukrainian territory, and the nuclear saber rattling.
Q. So is Putin just trying to appease some of his critics, or might he actually use a nuclear weapon?
The Russian leader is probably the only person who can answer this question with authority. Most nuclear experts say the likelihood of Russia actually using a nuclear weapon is still relatively low, but given Putin's current predicament, and his public statements, the threat is seen as increasing.
Bunn said his best estimate is that there's a 10 percent to 20 percent likelihood that Russia might use a nuke. While that's a pretty low probability for most things in life, when it comes to nuclear weapons, it is "intolerably high," Bunn said.
Q. How could a nuclear strike help Russia on the battlefield?
It's not clear that such an attack would give Russia a major military boost.
Russia has an estimated 2,000 small, low-yield, tactical nuclear weapons that could be used against specific targets — like a concentration of troops, a military base, perhaps a port or an air field.
However, Bunn notes that "one problem with using nuclear weapons, especially if you detonate them on the ground where they suck up a bunch of dirt and rock into the air, is the place where you use them ends up being uninhabitable because radioactive fallout."
Russia can do just as much damage, if not more, with a relentless barrage of conventional weapons. The Russian military has already devastated a number of Ukrainian cities with conventional firepower.
Bunn said if Russia uses a nuclear weapons, the intention may be mainly to intimidate Ukraine and the West.
"I think the biggest factor in the use of nuclear weapons is the fear they provoke," Bunn said. "Putin might hope that he could coerce the Ukrainians into accepting his terms, that he could coerce the West into backing off from supporting Ukraine."
Q. How are Ukraine and the U.S. reacting at this point?
A senior U.S. defense official told reporters Monday that the the U.S. is keeping close watch, and hasn't seen any Russian moves that would compel the U.S. to change its own nuclear posture.
Ukraine hasn't said much about Putin's most recent threat, but the country has a first-hand understanding of nuclear dangers following the 1986 accident at the Chernobyl nuclear power plant in Ukraine, which ultimately claimed thousands of lives.
While Ukraine has multiple nuclear power plants for civilian use, the country does not have nuclear weapons. Ukraine inherited a large nuclear arsenal when the Soviet Union broke up in 1991. But Ukraine gave up its nuclear weapons under a 1994 agreement under which Russia pledged to respect Ukraine's borders.
Q. What might the U.S. do if Russia actually set off a nuclear weapon?
President Biden's administration has warned of a powerful, though unspecified U.S. response. The U.S. president has sought to avoid a direct military confrontation with Russia, but a Russian nuclear strike could change the calculus.
According to Bunn, such an attack could lead the U.S. to hit Russian military targets, though he thinks it unlikely the U.S. would respond with nuclear weapons.
"People have talked about things like conventional attacks on Russian forces in Ukraine," he said. "Things that would be extremely unpleasant for the Russians and make the cost of using nuclear weapons higher than the plausible benefits."
Q. Beyond the battlefield, what kind of international response could Russia expect?
Russia is so far coping with international sanctions. But punitive measures would surely increase in the wake of a nuclear attack, and Russia's remaining partners might seek to distance themselves from Moscow.
The response of two countries, China and India, would be particularly important. China's ties with Russia were expanding, but Beijing is growing uncomfortable with the trajectory of the war. India has officially remained neutral and has been buying more Russian oil.
A Russian nuclear strike would likely lead both countries to reassess their current relationship with Moscow.
"Russia would really find itself completely isolated on the world stage," Bunn said.
A MARTINEZ, HOST:
Russian President Vladimir Putin has once again raised the possibility of deploying nuclear weapons in his war with Ukraine. He says he's not bluffing, but what are the chances he'll really do it? For more, we're joined by NPR national security correspondent Greg Myre. Greg, it's not the first time in this war that Vladimir Putin has talked about using nuclear weapons. Why is he talking about it again now?
GREG MYRE, BYLINE: Well, Ukraine is still gaining ground with these offensives in the east and the south of the country. This is putting pressure on Putin, especially from the hard-line pro-war camp in Russia. So all this has likely contributed to his recent escalation, the mobilization of more troops, the annexing of Ukrainian territory and this nuclear threat.
MARTINEZ: It's one thing to threaten using a nuclear weapon. It's another thing to actually use it. Can you give us some sense of the likelihood of him doing it?
MYRE: Yeah, Vladimir Putin is probably the only one that knows the exact possibility here. Most nuclear experts I've been talking to say the likelihood of Russia actually using such a weapon is still relatively low. And I spoke with Matthew Bunn at the Harvard Kennedy School, and I asked him to sort of put a number on it. He's studied nuclear issues throughout his career and served as a White House adviser. His best estimate is it's a 10 to 20% likelihood that Russia might use a nuke. Now, most things in life - that's a pretty low probability. But he says when it comes to nukes, this is intolerably high.
MARTINEZ: Yeah, 10 to 20%. Did he say how a strike could help Russia, though?
MYRE: Well, he pointed out Russia has all of these small, low-yield, tactical nukes that can be designed for a specific target - a concentration of troops, a military base, perhaps a port or an airfield. But he noted that Russia can attack these targets with just a large number of conventional weapons. And he says just look at the Ukrainian cities that have already been flattened. So Bunn thinks a nuclear strike, if it is used, may be intended more to intimidate as much to - as gain military advantage.
MATTHEW BUNN: I think the biggest factor in the use of nuclear weapons is the fear they provoke. Putin might hope that he could coerce the Ukrainians into accepting his terms, that he could coerce the West into backing off.
MARTINEZ: So how have the West and Ukraine reacted to this?
MYRE: Well, a senior U.S. defense official said the U.S. isn't seeing any Russian moves that would compel the U.S. to change its own nuclear posture. But if Russia does go nuclear, President Biden and his team have already warned Moscow that they will be on the end of a powerful, though unspecified, U.S. response. Now, Bunn says U.S. could very well target Russian military forces, which would be a big deal, bring added risk. But he thinks it's very unlikely the U.S. would respond with nukes.
BUNN: People have talked about things like conventional attacks on Russian forces in Ukraine, a variety of things that would be extremely unpleasant for the Russians and make the cost of using nuclear weapons higher than the plausible benefits.
MARTINEZ: So aside then - aside from the battlefield, what kind of a political and moral opposition could Russia expect to encounter?
BUNN: That seems certain. Russia's international isolation would deepen. Two important countries to look at, in particular - China and India. China has growing ties with Russia, but it's clearly becoming uncomfortable with aspects of the war. India has tried to remain neutral. By using a nuclear strike, Russia could lose both of them and become a true pariah.
MARTINEZ: That's NPR's Greg Myre. Greg, thanks a lot.
MYRE: My pleasure. Transcript provided by NPR, Copyright NPR.