On August 2, in a brazen attack on the arms control architecture forged by US and Soviet leaders during the Cold War era, the United States formally withdrew from the Intermediate-Range Nuclear Forces (INF) Treaty, a 1987 accord that bans the possession of ground-launched ballistic and cruise missiles with a range of between 500 and 5,500 kilometers (310 to 3,420 miles). Just two weeks later, on August 18, the Defense Department test-fired a cruise missile that would have violated the treaty, were the United States still in compliance. That test, involving a ground-based version of the sea-launched Tomahawk cruise missile, was intended less as a technology assessment than as a political statement—to demonstrate the Pentagon’s determination to rapidly field an array of treaty-non-compliant weapons and put China and Russia on the defensive. Unless halted by Congress, this drive will almost certainly spark a dangerous new arms race and dramatically narrow the “firebreak” between conventional and nuclear war.

To appreciate the extreme dangers posed by this new US missile drive, it is essential to grasp the distinctive nature of the INF treaty. Unlike strategic arms reduction and limitation treaties, like SALT I and II of the 1970s and the existing New START, which seek to restrain the intercontinental (“strategic”) nuclear arsenals of the major powers (that is, weapons aimed at each other’s homeland), the INF accord completely eliminated an entire class of weapons—in this case, missiles intended for use in a regional, or “theater” context, assumed to be Europe.

As viewed by Western strategists at the time, such weapons were intended as a “bridge” between conventional and nuclear conflict: In response to a potential massive Soviet assault that might overwhelm NATO positions in Central Europe, the United States would hold out the threat of quickly hurling nuclear weapons against enemy forces and command centers (thus, presumably, deterring any such Soviet attack). But the Soviets, fearing similar attacks from NATO, deployed theater nukes of their own, putting all of Europe at risk of nuclear annihilation. It soon became obvious to anti-nuclear activists in both Europe and the United States that any outbreak of conflict in Europe would quickly result in the rapid use of those non-strategic nukes, with all-out nuclear war sure to follow. As massive protests multiplied on both sides of the Atlantic, US and Soviet leaders began talking about limitations on theater weapons, finally agreeing to their elimination altogether. With their destruction—by the treaty’s deadline of June 1, 1991, a total of 2,692 of such weapons had been demolished—the risk of rapid escalation across the nuclear firebreak had been substantially reduced.

With the end of the Cold War and disappearance of superpower tensions, the prospect of nuclear escalation greatly diminished. As tensions between Washington, Moscow, and Beijing have heated up, however, those concerns have surfaced again. And that brings us back to the INF Treaty and the problem of the “bridge” between conventional and nuclear conflict.

In recent years, both Russia (which assumed the USSR’s treaty obligations) and the United States have accused the other of violating the INF treaty. The most serious charge has come from Washington, which claims that Russia has deployed a treaty-non-compliant ground-launched cruise missile, the 9M729, in its western regions, where it could reach targets in NATO territory. Moscow, for its part, claims that the US “Aegis Ashore” missile interceptor now deployed in Romania (and soon to be based in Poland), can be used to fire proscribed offensive weapons, although Washington insists it can only be used to launch defensive weapons designed to intercept an Iranian (or other “rogue state” missile). Efforts to resolve these discordant claims through negotiations came to naught.

The Trump administration, in the run-up to its August 2 announcement of withdrawal from the treaty, spoke a lot about Russian violations and the dangers they allegedly pose to NATO. But the missile test on August 18 revealed another motivation entirely: Far from fearing a few dozen Russian cruise missiles—which could, in any case, be neutralized by other weapons already in the US arsenal (such as air- and sea-launched cruise missiles)—the Defense Department seeks the freedom to field an array of treaty-non-compliant weapons of its own. In particular, the Pentagon would like hundreds, eventually thousands, of conventionally armed ground-based cruise and ballistic missiles that could be fired at critical Russian and Chinese military assets—air bases, air-defense radars, mobile missile systems, communications nodes, and so on—located on their national territory.

“We would like to deploy a capability sooner rather than later,” said newly installed Secretary of Defense Mark Esper on August 2, when asked, during a flight to Australia, to describe his plans for such missiles. “We want to develop this capability and making sure [sic] we can have long-range precision fires,” not only for Europe but also for Asia, given “how important an intermediate-range conventional weapon would be to [that] theater.”

Esper identified two such weapons his department was in the process of developing (bear in mind that initial work on these INF-non-compliant systems had begun when the United States was loudly complaining about Russian violations of the treaty): a ground-launched cruise missile, derived from an existing air- or sea-launched system like the Tomahawk; and a ballistic missile, called PrSM (pronounced “prism”), for Precision Strike Missile. The Pentagon requested $76 million for continued development of these systems in its Fiscal Year 2020 budget proposal, along with additional millions of dollars for longer-range follow-on weapons. Some of these more advanced projectiles are expected to be fitted with “boost-glide” delivery systems capable of flying at hypersonic speeds (more than five times the speed of sound).

Much secrecy surrounds the design and intended purpose of these missile systems, but from what can be deduced from comments by senior officials (like those made by Esper), the intent is to deploy these munitions in Europe and the Western Pacific, where they can be used for prompt attacks on high-value Chinese and Russian targets at the very outset of a conflict. This would then make it possible for slower-moving ships, planes, and ground forces to penetrate enemy territory with reduced risk of injury.

All this presupposes, of course, that acquiring the capacity to attack critical military installations deep within Chinese and Russian territory at the very onset of a crisis helps deters rash acts by those countries and so serves US security interests. Missing from this equation is the likelihood that both China and Russia are likely to respond by acquiring more offensive and defensive weapons of their own, thereby prompting reciprocal measures by the United States and sparking a costly new arms race.

Even more worrisome is the danger that any large-scale US missile attack on critical command facilities in China and Russia, even if conducted with conventionally armed weapons, might be interpreted as constituting the onset of a disarming US nuclear first strike. Once those missiles were launched, it would be nearly impossible for Chinese or Russian radars to determine what sort of warhead they carried, and their short flight duration—no more than 10 or 15 minutes—would give enemy decision-makers little time in which to decide what sort of countermeasures to take (before they themselves faced obliteration); fearing the worst, they might opt for a prompt nuclear response. That is exactly the sort rapid escalation scenario, overleaping the nuclear firebreak, that the INF treaty was intended to prevent.

It is also the fear of “decapitating” attacks of this sort that has fueled Russia’s drive to build a nuclear-armed, nuclear-powered cruise missile, called “Skyfall” in the West, that could be launched at a moment’s notice, circle the globe, and attack the US coastline. A test of the missile’s engine on August 8 at a site in northern Russia apparently failed, killing at least seven workers and releasing unknown amounts of radioactive material into the air and water.

Russia’s deployment of the 9M729, if confirmed, represents a significant violation of the INF treaty; China’s buildup of intermediate-range missiles on its coast opposite Taiwan poses an additional challenge. These issues are best resolved, however, through serious negotiations, not the rapid pursuit of additional war fighting capabilities. A US decision to deploy hundreds of ground-launched missiles aimed at the Chinese and Russian homelands, even if (initially) conventionally armed, can only lead to a dangerous arms race and increased risk of nuclear escalation. Fortunately, a majority in the House of Representatives agree with this assessment, and so have voted to exclude funding in the FY 2020 defense authorization bill for the missiles sought by Esper without further justification for their need. The Republican-controlled Senate, however, has shown no such reluctance. It is essential, then, that Democratic members of the Senate stand by their colleagues in the House and keep the missile exclusion intact when the two houses meet to resolve differences in the authorization bill.