New START, the last remaining major U.S.-Russia arms control treaty, is now confirmed dead. While there has been repeated talk about extending it or negotiating some kind of stopgap deal, interest in perpetuating the treaty has cratered. This is due in part to Washington’s growing skepticism about Russian compliance and, perhaps more importantly, U.S. President Donald Trump’s stated desire to pursue a new arms control framework of his own—one that would include China.

With New START gone, there are no longer any legal constraints preventing the United States and Russia from expanding their nuclear arsenals. What such an expansion might look like remains unclear. There are, however, some material constraints, and neither the United States nor Russia is currently well positioned to exploit the removal of limits in any dramatic way.

New START, the last remaining major U.S.-Russia arms control treaty, is now confirmed dead. While there has been repeated talk about extending it or negotiating some kind of stopgap deal, interest in perpetuating the treaty has cratered. This is due in part to Washington’s growing skepticism about Russian compliance and, perhaps more importantly, U.S. President Donald Trump’s stated desire to pursue a new arms control framework of his own—one that would include China.

With New START gone, there are no longer any legal constraints preventing the United States and Russia from expanding their nuclear arsenals. What such an expansion might look like remains unclear. There are, however, some material constraints, and neither the United States nor Russia is currently well positioned to exploit the removal of limits in any dramatic way.

Both countries have struggled to modernize their nuclear forces and production facilities. While each could draw from existing arsenals to increase their number of deployed missiles, neither is currently capable of engaging in a Cold War-style arms race. Even China—despite having spent the past decade modernizing every aspect of its nuclear weapons enterprise—is now facing delays. The U.S. Department of Defense’s recent China military power report, for instance, stated that China is currently struggling to build fast breeder reactors for producing plutonium.

The most troubling consequence of New START’s collapse is not that the United States and Russia will dramatically expand their arsenals in the near term. It is that in the long run, both the United States and Russia could modify their forces in other ways that destroy any remaining mutual trust and make returning to a future arms control process far more difficult.

It is often forgotten just how much of the United States’ and Russia’s nuclear forces—including how weapons are categorized, where they are based, and how they are prepared for combat—has been shaped by decades of arms control treaty mechanisms designed to minimize cheating and improve accountability. New START and the treaties that came before it, dating back to 1972, imposed detailed restrictions and definitions intended to ensure that verification of both sides’ compliance was feasible.

These provisions mattered because verification was—and remains—difficult. During the Cold War, remote detection via national technical means was expensive, slow, and not of particularly good quality. Even with on-site inspections, there was always a risk that missiles could be hidden, moved, or disguised.

To mitigate these challenges, arms control treaties have established clear definitions for things such as missile bases, required each side to declare their locations, prohibited operating missiles from undeclared areas, and under New START barred deliberate concealment of nuclear forces from the other’s watching satellites.

At the time, these rules did not significantly degrade the survivability of mobile nuclear forces because the available technology could not quickly track missiles in the field. Today, that is no longer the case. Government and commercial remote-sensing capabilities are far more technically advanced and robust than during the Cold War. Advances in cyberweapons add a new layer of risk: On-site inspections could expose vulnerabilities in production or deployment infrastructure that might later be exploited.

If one side believes the other intends to exploit transparency measures in this way to cement their nuclear supremacy—a concern Russia and China have repeatedly raised about the United States—then revealing any information at all could be a serious hazard to a state’s ability to withstand a nuclear first strike. The rational response would be to seal off nuclear forces from external observation altogether.

These are precisely the concerns that have driven China’s nuclear posture. Never bound by arms control treaties, China developed its nuclear forces unconstrained by any verification mechanism. Unlike the United States and Russia, which openly declare and display the locations of their nuclear forces, China uses concealment, deception, and secrecy to ensure the survivability of its arsenal. For instance, it disguises its mobile forces as box trucks (or, hilariously, mail trucks) and utilizes specially built secret tunnels to house its intercontinental ballistic missiles—both of which would be considered New START violations.

Without an arms control treaty that constrains this kind of obfuscation, the United States and Russia are free to adopt similar measures. If, for example, Russia believed that advances in U.S. remote detection threaten the survivability of its mobile forces, it could mirror China’s behavior and alter its basing and operating practices in ways that were previously prohibited—moving its nuclear forces around more frequently, operating from undeclared locations, or concealing its exact number of deployed warheads.

These issues will come to a head if negotiations on a successor treaty drag on or if Trump insists on bringing China into the process. U.S. Secretary of State Marco Rubio acknowledged this explicitly on Friday: “We understand that this process can take time. Past agreements, including New START, took years to negotiate and were built upon decades of precedent. They were also between two powers, not three or more.”

If negotiating a new arms control treaty among three states is truly something that is going to take years, if not a decade, then the arms control window may already be closing. The longer this dynamic persists, the greater the risk that both sides will drift from postures designed to maximize verification toward ones that are inherently, and perhaps intentionally, difficult to verify.

Such changes would, in turn, breed further distrust, as efforts to enhance survivability of mobile forces could be interpreted as attempts to mask force size or evade monitoring altogether. The result would be a feedback loop of mistrust that would make any future arms control measures progressively harder. Attempting to rope in China would make the entire process grind to a halt, as the United States would likely demand verification mechanisms that would be fundamentally incompatible with China’s current basing method.

These are not easy problems to solve. They may, in fact, be unsolvable given advances in technology for tracking mobile forces and the development of cyberweapons. If even the most mundane piece of information about an enemy’s nuclear force is now a potential attack vector, negotiating what can safely be revealed becomes extraordinarily difficult.

Ultimately, the biggest risks stemming from the collapse of New START have little to do with warhead or delivery vehicle numbers. Rather, they lie in the gradual erosion of trust between the United States and Russia, compounded by a changing technical reality that incentivizes posture changes. How this will unfold is impossible to predict. What is clear, however, is that negotiating the arms control treaty of tomorrow may be far more difficult than the Trump administration expects. As Rubio said, it’s a process that will take years. We should be prepared for the possibility that it may take a decade for any new arms control treaty to enter into force—and for all major nuclear states to become more evasive in the meantime.