Russia’s invasion of Ukraine continues with violence and death. Read the latest developments here. Facing stronger-than-expected resistance from Ukrainians, Russia is also seeing intensified isolation from much of the rest of the world: But Putin’s rhetoric has also intensified to include direct reference to his nation’s vast nuclear stockpile, placing the country on its highest state of alert and forcing an appraisal of the equilibrium that keeps nuclear-armed countries from destroying themselves and the world. What did Putin say? “Top officials in leading NATO countries have allowed themselves to make aggressive comments about our country, therefore I hereby order the Minister of Defense and the chief of the General Staff to place the Russian Army Deterrence Force on combat alert,” Putin said in a televised meeting with top Russian defense officials on Sunday. Russia’s nuclear weapons are a part of its “deterrence” strategy. Russia took control of arms from other former Soviet republics, including Ukraine and Belarus, in the 1990s. Now Russia has invaded Ukraine – and Belarus, which is allied with Moscow, plans to renounce its non-nuclear status and could theoretically allow Russia to bring nuclear weapons back into the country. Should people be worried? President Joe Biden had a simple answer on Monday when asked by reporters if Americans should be concerned about the prospect of nuclear war. “No,” he said. Is this an unprecedented nuclear threat? The threat isn’t unprecedented. I talked to Matthew Fuhrmann, who along with Todd Sechser, wrote the 2017 book, “Nuclear Weapons and Coercive Diplomacy.” They documented 19 instances of nuclear threats and coercive language in the post-World War II era. These include Soviet leaders like Nikita Khrushchev telling the then-US ambassador in 1959, “The West seems to forget that a few Russian missiles could destroy all of Europe.” They also include former President Richard Nixon, employing his madman theory of foreign policy, wanting the North Vietnamese to be told his aides believed, “We can’t restrain him when he’s angry – and he has his hand on the nuclear button.” Will Putin’s threats work now? “The track record for nuclear blackmail is not great,” said Fuhrmann in an email. “In many cases, attempts to bully other countries by raising the specter of nuclear war plainly failed, like in Khrushchev’s threats over Berlin. In other cases, like the crises between the US and China over Taiwan in the 1950s, a country got its way after making nuclear threats but it wasn’t clear that those threats played a decisive role.” That said, the US is certainly not entering the war Russia has waged on Ukraine, and it is not creating a no-fly zone. Putin must realize that using nuclear weapons will bring them upon him and his people. “To threaten nukes cost him nothing. To use them, that will cost him everything,” said the former commander of US Army forces in Europe, retired Lt. Gen. Ben Hodges, appearing on CNN on Monday. What is Russia’s nuclear stockpile? Russia’s total nuclear stockpile is larger than the United States’, at around 6,250 total nuclear warheads, according to the Arms Control Association. The US has more than 5,500. Most of those warheads in both countries are not deployed on missiles or at bases. According to an assessment by the Arms Control Association, in terms of deployed nuclear warheads: No other country known or thought to have nuclear weapons – the United Kingdom, France, Israel, Pakistan, India, China and North Korea – has anywhere near those numbers of warheads. Does Putin understand the implications of nuclear war? “You kind of get the sense that either he doesn’t care or he’s not completely in touch with reality,” said Tom Collina, policy director at the Ploughshares Fund, which pushes for the elimination of dangers posed by nuclear weapons. “You know, does he fully understand the consequences of what he’s doing or has he become one of these autocrats that’s so sort of divorced from reality,” wondered Collina in a phone call when I asked him how Putin’s rhetoric has changed over the past week. Sechser says Putin may not have thought it all through. “Russia has now played most of its escalatory cards, and doesn’t have many tools left for resolving this crisis in its favor. The nuclear alert seems like more an act of frustration than a calculated tactical move,” he said in an email. “If the nuclear alert was intended to coerce the United States and Europe into tempering economic sanctions or abandoning Ukraine, it failed. If anything, it has served to further inflame world opinion against Russia,” Sechser added. The US has nuclear weapons in Europe What has long irked Putin is the US has around 100 nuclear weapons stored in Europe at NATO bases in Italy, Germany, Turkey, Belgium and the Netherlands. He fears the US could place nuclear weapons in NATO countries farther east, closer to Russia. The US weapons in Europe are not thought to be armed, according to the Center for Arms Control and Non-Proliferation, but rather stored underground. They would need to be loaded onto fighter jets for use. A new version of the START Treaty first enacted in 2011 and extended in 2021 caps the US and Russia at 1,550 deployed nuclear warheads each. There are thousands of additional warheads that could be called up. What is Russia’s policy on nuclear weapons? While during the Cold War, Russia employed a “no-first-use” policy toward nuclear weapons, a series of published policy positions on the issue have, since the 1990s, suggested the country could use nuclear weapons in a localized war or if it felt its sovereignty or national integrity were threatened. Putin endorsed a new “deterrent” strategy in June 2020 that allowed for the use of nuclear weapons in response to a non-nuclear attack on Russia that threatened its existence. It’s notable that Russia has, in the view of the US, lied about threats posed to it by Ukraine and the West. What is the Biden administration saying? The Biden administration is being very careful to support Ukraine without becoming directly involved in the military fight. And it is making very clear the US has not changed its own nuclear threat level. Everything the administration says is focused on pushing Russia to retreat without using the US military. That’s why the US has rejected Ukrainian President Volodymyr Zelensky’s plea to create a no-fly zone over Ukraine. “What we want to do right now is reduce the rhetoric and de-escalate,” said White House press secretary Jen Psaki on Monday. What is the US policy on using nuclear weapons? The US also does not have a “no-first-use” policy and allows for the “sole authority” of the President to use nuclear weapons, and most presidents have said the “sole purpose” would be nuclear deterrence. Former President Donald Trump seemed to expand the universe of possible nuclear scenarios to include “significant non-nuclear strategic attacks.” You’ve probably read about the nuclear football that is carried near the President at all times. If you haven’t, you should. The Biden administration is expected to complete its own broad Nuclear Posture Review, traditionally done by new presidents, early this year. The review lays out an administration’s approach to nuclear weapons policy. These reviews are often largely classified. As a candidate, Biden suggested he would pursue a “sole purpose” nuclear strategy, which means the nuclear force can only be used to deter or retaliate for a nuclear attack against the US and its allies. Just before the outbreak of the war in Ukraine, experts were not expecting a major departure from the policies of previous presidents. There is no room for error Collina says that his fear is a nuclear war started by accident. “My concern is that as they increase the alert level, or the readiness level of their nuclear forces, if they are, then that makes it easier to stumble into nuclear war by mistake,” he said, pointing out that it has been 77 years since the US was the first and last country to detonate an atomic bomb. A nuclear weapon detonated during a war now would cause a reevaluation by the powers that have a stockpile. “It would be just a devastating catastrophic event on the ground for those people there, but also for the world going forward,” he said.