Once upon a time, when choosing a new president, a factor for many voters was the perennial question: “Whose finger do you want on the nuclear button?” Of all the responsibilities of America’s top executive, none may be more momentous than deciding whether, and under what circumstances, to activate the “nuclear codes”—the secret alphanumeric messages that would inform missile officers in silos and submarines that the fearful moment had finally arrived to launch their intercontinental ballistic missiles (ICBMs) toward a foreign adversary, igniting a thermonuclear war.

Until recently in the post–Cold War world, however, nuclear weapons seemed to drop from sight, and that question along with it. Not any longer. In 2016, the nuclear issue is back big time, thanks both to the rise of Donald Trump (including various unsettling comments he’s made about nuclear weapons) and actual changes in the global nuclear landscape.

With passions running high on both sides in this year’s election and rising fears about Donald Trump’s impulsive nature and Hillary Clinton’s hawkish one, it’s hardly surprising that the “nuclear button” question has surfaced repeatedly throughout the campaign. In one of the more pointed exchanges of the first presidential debate, Hillary Clinton declared that Donald Trump lacked the mental composure for the job. “A man who can be provoked by a tweet,” she commented, “should not have his fingers anywhere near the nuclear codes.” Donald Trump has reciprocated by charging that Clinton is too prone to intervene abroad. “You’re going to end up in World War III over Syria,” he told reporters in Florida last month.

For most election observers, however, the matter of personal character and temperament has dominated discussions of the nuclear issue, with partisans on each side insisting that the other candidate is temperamentally unfit to exercise control over the nuclear codes. There is, however, a more important reason to worry about whose finger will be on that button this time around: at this very moment, for a variety of reasons, the “nuclear threshold”—the point at which some party to a “conventional” (non-nuclear) conflict chooses to employ atomic weapons—seems to be moving dangerously lower.

Not so long ago, it was implausible that a major nuclear power—the United States, Russia, or China—would consider using atomic weapons in any imaginable conflict scenario. No longer. Worse yet, this is likely to be our reality for years to come, which means that the next president will face a world in which a nuclear decision-making point might arrive far sooner than anyone would have thought possible just a year or two ago—with potentially catastrophic consequences for us all.

No less worrisome, the major nuclear powers (and some smaller ones) are all in the process of acquiring new nuclear arms, which could, in theory, push that threshold lower still. These include a variety of cruise missiles and other delivery systems capable of being used in “limited” nuclear wars—atomic conflicts that, in theory at least, could be confined to just a single country or one area of the world (say, Eastern Europe) and so might be even easier for decision-makers to initiate. The next president will have to decide whether the U.S. should actually produce weapons of this type and also what measures should be taken in response to similar decisions by Washington’s likely adversaries.

Lowering the Nuclear Threshold

During the dark days of the Cold War, nuclear strategists in the United States and the Soviet Union conjured up elaborate conflict scenarios in which military actions by the two superpowers and their allies might lead from, say, minor skirmishing along the Iron Curtain to full-scale tank combat to, in the end, the use of “battlefield” nuclear weapons, and then city-busting versions of the same to avert defeat. In some of these scenarios, strategists hypothesized about wielding “tactical” or battlefield weaponry—nukes powerful enough to wipe out a major tank formation, but not Paris or Moscow—and claimed that it would be possible to contain atomic warfare at such a devastating but still sub-apocalyptic level. (Henry Kissinger, for instance, made his reputation by preaching this lunatic doctrine in his first book, Nuclear Weapons and Foreign Policy.) Eventually, leaders on both sides concluded that the only feasible role for their atomic arsenals was to act as deterrents to the use of such weaponry by the other side. This was, of course, the concept of “mutually assured destruction,” or—in one of the most classically apt acronyms of all times: MAD. It would, in the end, form the basis for all subsequent arms control agreements between the two superpowers.

Anxiety over the escalatory potential of tactical nuclear weapons peaked in the 1970s when the Soviet Union began deploying the SS-20 intermediate-range ballistic missile (capable of striking cities in Europe, but not the U.S.) and Washington responded with plans to deploy nuclear-armed, ground-launched cruise missiles and the Pershing-II ballistic missile in Europe. The announcement of such plans provoked massive antinuclear demonstrations across Europe and the United States. On December 8, 1987, at a time when worries had been growing about how a nuclear conflagration in Europe might trigger an all-out nuclear exchange between the superpowers, President Ronald Reagan and Soviet leader Mikhail Gorbachev signed the Intermediate-Range Nuclear Forces (INF) Treaty.

That historic agreement—the first to eliminate an entire class of nuclear delivery systems—banned the deployment of ground-based cruise or ballistic missiles with a range of 500 and 5,500 kilometers and required the destruction of all those then in existence. After the collapse of the Soviet Union, the Russian Federation inherited the USSR’s treaty obligations and pledged to uphold the INF along with other U.S.-Soviet arms control agreements. In the view of most observers, the prospect of a nuclear war between the two countries practically vanished as both sides made deep cuts in their atomic stockpiles in accordance with already existing accords and then signed others, including the New START, the Strategic Arms Reduction Treaty of 2010.

Today, however, this picture has changed dramatically. The Obama administration has concluded that Russia has violated the INF treaty by testing a ground-launched cruise missile of prohibited range, and there is reason to believe that, in the not-too-distant future, Moscow might abandon that treaty altogether. Even more troubling, Russia has adopted a military doctrine that favors the early use of nuclear weapons if it faces defeat in a conventional war, and NATO is considering comparable measures in response. The nuclear threshold, in other words, is dropping rapidly.

Much of this is due, it seems, to Russian fears about its military inferiority vis-à-vis the West. In the chaotic years following the collapse of the USSR, Russian military spending plummeted and the size and quality of its forces diminished accordingly. In an effort to restore Russia’s combat capabilities, President Vladimir Putin launched a multi-year, multi-billion-dollar expansion and modernization program. The fruits of this effort were apparent in the Crimea and Ukraine in 2014, when Russian forces, however disguised, demonstrated better fighting skills and wielded better weaponry than in the Chechnya wars a decade earlier. Even Russian analysts acknowledge, however, that their military in its current state would be no match for American and NATO forces in a head-on encounter, given the West’s superior array of conventional weaponry. To fill the breach, Russian strategic doctrine now calls for the early use of nuclear weapons to offset an enemy’s superior conventional forces.

To put this in perspective, Russian leaders ardently believe that they are the victims of a U.S.-led drive by NATO to encircle their country and diminish its international influence. They point, in particular, to the build-up of NATO forces in the Baltic countries, involving the semi-permanent deployment of combat battalions in what was once the territory of the Soviet Union, and in apparent violation of promises made to Gorbachev in 1990 that NATO would not do so. As a result, Russia has been bolstering its defenses in areas bordering Ukraine and the Baltic states, and training its troops for a possible clash with the NATO forces stationed there.

This is where the nuclear threshold enters the picture. Fearing that it might be defeated in a future clash, its military strategists have called for the early use of tactical nuclear weapons, some of which no doubt would violate the INF Treaty, in order to decimate NATO forces and compel them to quit fighting. Paradoxically, in Russia, this is labeled a “de-escalation” strategy, as resorting to strategic nuclear attacks on the U.S. under such circumstances would inevitably result in Russia’s annihilation. On the other hand, a limited nuclear strike (so the reasoning goes) could potentially achieve success on the battlefield without igniting all-out atomic war. As Eugene Rumer of the Carnegie Endowment of International Peace explains, this strategy assumes that such supposedly “limited” nuclear strikes “will have a sobering effect on the enemy, which will then cease and desist.”

To what degree tactical nuclear weapons have been incorporated into Moscow’s official military doctrine remains unknown, given the degree of secrecy surrounding such matters. It is apparent, however, that the Russians have been developing the means with which to conduct such “limited” strikes. Of greatest concern to Western analysts in this regard is their deployment of the Iskander-M short-range ballistic missile, a modern version of the infamous Soviet-era “Scud” missile (used by Saddam Hussein’s forces during the Iran-Iraq war of 1980-1988 and the Persian Gulf War of 1990-1991). Said to have a range of 500 kilometers (just within the INF limit), the Iskander can carry either a conventional or a nuclear warhead. As a result, a targeted country or a targeted military could never be sure which type it might be facing (and might simply assume the worst). Adding to such worries, the Russians have deployed the Iskander in Kaliningrad, a tiny chunk of Russian territory wedged between Poland and Lithuania that just happens to put it within range of many western European cities.

In response, NATO strategists have discussed lowering the nuclear threshold themselves, arguing—ominously enough—that the Russians will only be fully dissuaded from employing their limited-nuclear-war strategy if they know that NATO has a robust capacity to do the same. At the very least, what’s needed, some of them claim, is a more frequent inclusion of nuclear-capable or dual-use aircraft in exercises on Russia’s frontiers to “signal” NATO’s willingness to resort to limited nuclear strikes, too. Again, such moves are not yet official NATO strategy, but it’s clear that senior officials are weighing them seriously.

Just how all of this might play out in a European crisis is, of course, unknown, but both sides in an increasingly edgy standoff are coming to accept that nuclear weapons might have a future military role, which is, of course, a recipe for almost unimaginable escalation and disaster of an apocalyptic sort. This danger is likely to become more pronounced in the years ahead because both Washington and Moscow seem remarkably intent on developing and deploying new nuclear weapons designed with just such needs in mind.

The New Nuclear Armaments

Both countries are already in the midst of ambitious and extremely costly efforts to “modernize” their nuclear arsenals. Of all the weapons now being developed, the two generating the most anxiety in terms of that nuclear threshold are a new Russian ground-launched cruise missile (GLCM) and an advanced U.S. air-launched cruise missile (ALCM). Unlike ballistic missiles, which exit the Earth’s atmosphere before returning to strike their targets, such cruise missiles remain within the atmosphere throughout their flight.

American officials claim that the Russian GLCM, reportedly now being deployed, is of a type outlawed by the INF Treaty. Without providing specifics, the State Department indicated in a 2014 memo that it had “a range capability of 500 km [kilometers] to 5,500 km,” which would indeed put it in violation of that treaty by allowing Russian combat forces to launch nuclear warheads against cities throughout Europe and the Middle East in a “limited” nuclear war.

The GLCM is likely to prove one of the most vexing foreign policy issues the next president will face. So far, the White House has been reluctant to press Moscow too hard, fearing that the Russians might respond by exiting the INF Treaty altogether and so eliminate remaining constraints on its missile program. But many in Congress and among Washington’s foreign policy elite are eager to see the next occupant of the Oval Office take a tougher stance if the Russians don’t halt deployment of the missile, threatening Moscow with more severe economic sanctions or moving toward countermeasures like the deployment of enhanced anti-missile systems in Europe. The Russians would, in turn, undoubtedly perceive such moves as threats to their strategic deterrent forces and so an invitation for further weapons acquisitions, setting off a fresh round in the long-dormant Cold War nuclear arms race.

On the American side, the weapon of immediate concern is a new version of the AGM-86B air-launched cruise missile, usually carried by B-52 bombers. Also known as the Long-Range Standoff Weapon (LRSO), it is, like the Iskander-M, expected to be deployed in both nuclear and conventional versions, leaving those on the potential receiving end unsure what might be heading their way. In other words, as with the Iskander-M, the intended target might assume the worst in a crisis, leading to the early use of nuclear weapons. Put another way, such missiles make for twitchy trigger fingers and are likely to lead to a heightened risk of nuclear war, which, once started, might in turn take Washington and Moscow right up the escalatory ladder to a planetary holocaust.

No wonder former Secretary of Defense William J. Perry called on President Obama to cancel the ALCM program in a recent Washington Post op-ed piece. “Because they… come in both nuclear and conventional variants,” he wrote, “cruise missiles are a uniquely destabilizing type of weapon.” And this issue is going to fall directly into the lap of the next president.

The New Nuclear Era

Whoever is elected on November 8th, we are evidently all headed into a world in which Trumpian-style itchy trigger fingers could be the norm. It already looks like both Moscow and Washington will contribute significantly to this development—and they may not be alone. In response to Russian and American moves in the nuclear arena, China is reported to be developing a “hypersonic glide vehicle,” a new type of nuclear warhead better able to evade anti-missile defenses—something that, at a moment of heightened crisis, might make a nuclear first strike seem more attractive to Washington. And don’t forget Pakistan, which is developing its own short-range “tactical” nuclear missiles, increasing the risk of the quick escalation of any future Indo-Pakistani confrontation to a nuclear exchange. (To put such “regional” dangers in perspective, a local nuclear war in South Asia could cause a global nuclear winter and, according to one study, possibly kill a billion people worldwide, thanks to crop failures and the like.)

And don’t forget North Korea, which is now testing a nuclear-armed ICBM, the Musudan, intended to strike the Western United States. That prompted a controversial decision in Washington to deploy THAAD (Terminal High Altitude Area Defense) anti-missile batteries in South Korea (something China bitterly opposes), as well as the consideration of other countermeasures, including undoubtedly scenarios involving first strikes against the North Koreans.

It’s clear that we’re on the threshold of a new nuclear era: a time when the actual use of atomic weapons is being accorded greater plausibility by military and political leaders globally, while war plans are being revised to allow the use of such weapons at an earlier stage in future armed clashes.

As a result, the next president will have to grapple with nuclear weapons issues—and possible nuclear crises—in a way unknown since the Cold War era. Above all else, this will require both a cool head and a sufficient command of nuclear matters to navigate competing pressures from allies, the military, politicians, pundits, and the foreign policy establishment without precipitating a nuclear conflagration. On the face of it, that should disqualify Donald Trump. When questioned on nuclear issues in the first debate, he exhibited a striking ignorance of the most basic aspects of nuclear policy. But even Hillary Clinton, for all her experience as secretary of state, is likely to have a hard time grappling with the pressures and dangers that are likely to arise in the years ahead, especially given that her inclination is to toughen U.S. policy toward Russia.

In other words, whoever enters the Oval Office, it may be time for the rest of us to take up those antinuclear signs long left to molder in closets and memories, and put some political pressure on leaders globally to avoid strategies and weapons that would make human life on this planet so much more precarious than it already is.