In 2021, U.S. president Joe Biden and Russian president Vladimir Putin said that nuclear war should never be fought and, if fought, could never be won. Many then assumed the statement reflected twin cautionary deterrent policies from both countries, with the chances of future nuclear weapons use significantly receding.

It is indeed true that the first statement—nuclear weapons should never be used—is the object of U.S. and NATO deterrent policy.

However, the second idea, that if nuclear weapons are ever used no one is going to come out the victor, misses the key point about credible deterrence: retaliating against an enemy that uses nuclear weapons against the United States is only credible if we mean it. Otherwise, it’s simply a bluff. As highlighted by at least four Nuclear Posture Reviews since 1994, the United States believes deterrence absolutely relies on the U.S. retaliatory use of nuclear weapons, precisely what the United States “will do in response” to aggression.

This is where confusion may now exist. For some global zero advocates, U.S. deterrent doctrine even including a retaliatory nuclear strike by the United States is often described as “warfighting” and needs to be stricken from U.S. security doctrine.

But if a retaliatory threat is a sheer bluff, then deterrence will have no effect. And furthermore, if it is assumed that any retaliatory use of nuclear weapons no matter how limited will escalate to an all-out massive exchange of nuclear weapons, then the U.S. threat of retaliation amounts to little more than a non-credible threat of mutual suicide. And without a credible deterrent, strategic stability is undermined, and war becomes more likely.

Thus, U.S. deterrent strategy and policy need to be constantly “re-established,” even if U.S. retaliatory strategy remains ambiguous as to exactly under what conditions the United States might use nuclear force. In short, if a retaliatory strike is dismissed as immoral “warfighting,” and thus outside U.S. strategy, what then is the point of the retaliatory nuclear strike threat to begin with?

Now it is true that since the dawn of the nuclear age some seven decades ago, the U.S. deterrent strategy has not been fixed. Strategy can be amended or updated.

A retaliatory strategy has usually been described in U.S. nuclear official documents as aimed at stopping a conflict at the earliest time and at the lowest possible level of conflict.

This was not always the case. For example, U.S. nuclear deterrent policy in the early stages of the nuclear era started as a single option policy of massive retaliation, particularly during the Eisenhower administration where the threat of a Soviet invasion of Western Europe was considered the primary threat the West faced. NATO could not match huge Soviet conventional forces on the European continent as costs would have been astronomical. Markedly less expensive nuclear weapons were the equalizer—they allowed the United States to maintain deterrence at a far less cost, including by fielding multiple thousands of regional battlefield nuclear weapons on the European continent.

As the United States graduated to a strategic force of more accurate, fast-flying intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs), our newly created triad was designed to retaliate against Soviet homeland military targets, not necessarily just battlefield targets. Much of this change was initiated during the Kennedy administration under the policy known as “flexible response.” This was to avoid being beholden to the Eisenhower era’s massive nuclear retaliation, which came to be seen as a less credible strategy.

But holding at risk the Soviet’s military assets—while far more moral than threatening to burn Russian cities to the ground—had implications for stability. What if the Soviets or Americans simply went first and tried to disarm the other guy? Holding an enemy’s nuclear military assets was key to deterrence, but if a disarming first strike looked achievable, any crisis might lead to the use of nuclear force.

So, U.S. nuclear forces had to be survivable. For example, in the 1950s General Curtis LeMay, chief of staff for the U.S. Air Force, was worried that a pre-emptive Soviet strike on just fourteen U.S. bunkers—where the U.S. air-dropped gravity bombs were stored—could totally disarm the United States.

It was thus the Air Force began the effort to seek a more survivable force by developing survivable land-based missiles to be deployed in hardened silos in the sovereign United States. Unlike shorter-range U.S. missiles in Turkey, for example, the new Minuteman missiles that were first deployed in October 1962 could strike the Soviet Union even if launched from the United States.

That is why Kennedy traded the United States’ Turkey-based Jupiter missiles away.

In addition, the new Minuteman missiles were solid-fueled, ready at any time to be launched should the U.S. president so order, without having to undergo a lengthy refueling process every time prior to launch.

Then the scientists at Lawrence Livermore nuclear lab developed a truly revolutionary capability: a nuclear missile warhead small enough to fit on newly-acquired submarines, which in turn had to patrol far out into the ocean to reach Soviet targets.

By contrast, the Soviets would develop submarine “boomers” with bigger missiles. This enabled Soviet sub missiles to reach the U.S. continent even if launched adjacent to sub-bases in Soviet-controlled bastions from which they usually operated.

While U.S. submarines are highly survivable and thus designed to retaliate, Soviet systems were designed to enable a pre-emptive strike against the United States, even if launched from a normal, day-to-day operational tempo.

With the projected Soviet deployment of over 10,000 strategic warheads by the 1980s looming even under the 1972 and 1979 Strategic Arms Limitation Talks (SALT) nuclear arms deals, the United States faced a heightened threat from the Soviets. Moscow, unlike Washington, could, without warning, destroy most of the United States’ ICBMs and bomber and submarine bases, and still have multiple thousands of warheads left with which to hold US cities hostage.

This gap was termed the “window of vulnerability,” and prompted Ronald Reagan to replace “détente” and “peaceful coexistence” with a “peace through strength” policy. Such a policy had three parts: first, modernize and make flexible an aging U.S. deterrent; second, push for big arms control reductions, at least 50 percent in strategic nuclear forces including banning multiple-warhead ICBMs; and third, plan to build missile defenses that would hugely complicate Soviet attack plans.

The strategy worked, and there are still appliable lessons from Reagan’s successful policy.

First, the end of the Soviet empire and the Cold War did not magically diminish or end nuclear threats.

Second, the United States mistakenly took a long post-Cold War acquisition holiday and that is why its ongoing nuclear deterrent modernization effort is so compressed.

Third, even as Moscow bought time by agreeing to reduce its nuclear weapons under the 1991 Strategic Arms Reduction Treaty (START), 2002 Moscow, and 2010 New START treaties, Russian nuclear threats accelerated, with Moscow building twenty-five to twenty-seven new strategic nuclear systems, now more than 80 percent complete.

Fourth, and most worrisome, Moscow adopted a new nuclear strategy in 1997-9. Under a doctrine of “escalate to win,” Moscow decided a nuclear war could be fought and could be won, but not necessarily with an all-out Armageddon-type attack. Instead, Moscow has sought to leverage the limited use of regional or theater nuclear weapons.

Now some U.S. “experts” dismissed the new doctrine as only rhetorical fodder for Putin’s domestic political supporters. Others, including former Office of the Secretary of Defense official Brad Roberts and the commander of U.S. Strategic Command General John Hyten, concluded the Russian policy of “escalate to win” was a very real new Russian theory of victory. The objective was to coerce or extort the United States to stand down in a crisis or surrender quickly in a conventional conflict.

In short, despite the end of the “Cold War,” Moscow still was willing to use or threaten to use military force, even recklessly and even at the nuclear level.

We have repeatedly seen this occur in the post-Soviet space. For example, in 2008 and 2014 in Georgia and Ukraine, respectively, Russia sent an unmistakable message that gray zone tactics including elements of guerilla war and cyber subversion were in its arsenal of aggression. Coercive nuclear threats continued to be instruments of statecraft. After all, the Russian attacks were largely undertaken with impunity.

This has been even more evident during Russia’s 2022 Ukraine invasion, where Moscow has successfully employed nuclear threats to deter the United States, even leading Washington to take its nuclear deterrent off the table in defense of Ukraine.

And this kind of nuclear brinksmanship is not unique to Russia—it is being matched elsewhere. For example, China over the past year has explicitly threatened Japan and Australia with missile strikes should either country militarily support Taiwan. North Korea has also tested multiple ballistic missiles and announced that such nuclear-armed missiles are not just a retaliatory deterrent but also could be used pre-emptively. Iran, too, continues to violate the Joint Comprehensive Plan of Action and ramp up its nuclear program with impunity.