I read Adam Lowther and Hunter Hustus’s January 2 reply to me, “Don’t Toss the Bomb,” with great interest. But they fail to make a persuasive case against my points in “Fewer Nukes Don’t Mean More Danger.” The United States has substantial room to reduce its nuclear arsenal, without risk to U.S. or allied security interests.

Lowther and Hustus write that my recent piece compares apples and oranges when relating the size of the U.S. nuclear arsenal to that of third countries. It is unclear why they make such an assertion. My article suggested that the United States and Russia each reduce to no more than 2,000-2,500 total nuclear weapons, of which 1,000 would be deployed strategic warheads, down from the 1,550 deployed strategic warheads allowed each side by the 2010 New Strategic Arms Reduction Treaty (New START). The article compared the resulting U.S. total nuclear arsenal (2,000-2,500) against the total nuclear arsenals of France (300) and China (250)—the third and fourth largest nuclear weapons states—and concluded that the United States would have around eight times as many weapons as any third power. That is an apples-to-apples comparison.

Contrary to Lowther and Hustus’s claim, the total U.S. arsenal size would allow for a significant hedge against unforeseen developments. Under the proposed 2,000-2,500 limit on total nuclear weapons, the United States could maintain 1,000-1,500 non-strategic (tactical) nuclear weapons and non-deployed (reserve) strategic weapons in addition to the 1,000 deployed strategic warheads.

This arsenal would allow plenty of slack to meet new challenges. The U.S. military is downloading most of its intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) so that they carry fewer warheads than their maximum capacity. Minuteman III ICBMs will be deployed with a single warhead, even though two-thirds of them can carry multiple warheads. The average Trident II SLBM will carry four or five warheads, although the Trident II has a maximum capacity of eight warheads. The United States could readily add many hundreds of additional strategic warheads to its deployed ICBM and SLBM forces were New START to break down.

Lowther and Hustus note that the Cold War is over. No argument here. They also write that the United States must maintain “the capability—and will—to deter multiple adversaries simultaneously.” We agree on that point as well. Deterrence has become more complex with the transition from the binary mutual deterrence relationship that existed between the United States and Soviet Union during the Cold War to one in which Washington faces several possible adversaries armed with nuclear weapons.

But Lowther and Hustus fail to answer the real world questions I posed in my December 12 article: Which potential adversary would act differently if the United States had “only” 2,500 nuclear weapons? Would North Korea adopt a more aggressive posture if the United States had just three hundred times as many nuclear weapons as it, instead of five hundred times as many? The answers to these questions are “no one” and “no.”

A stockpile of 2,500 nuclear weapons should suffice to deter America’s possible nuclear adversaries: Russia, China, and North Korea.

Lowther and Hustus argue that numbers have to derive from strategy. Again we agree. The Joint Chiefs of Staff endorsed the proposal made by President Obama last June in Berlin to lower the New START ceiling of 1,550 deployed strategic warheads by one-third, i.e., to 1,000-1,100 warheads. That presumably reflects their assessment that the number would support nuclear deterrence requirements and war plans.

Lowther and Hustus appear to reject the notion of equality in nuclear weapons levels. Were the United States to seek numerical superiority, how do they expect Russia to respond? That would seem to be a recipe for a classical nuclear arms race, to neither side’s benefit. As for third countries, when U.S. and Russian nuclear weapons levels are more than an order of magnitude greater than that of any third country, the two superpowers have room to reduce.

Addressing extended deterrence, Lowther and Hustus note that NATO has expressed its desire to remain a nuclear alliance. That was the conclusion of the 2012 NATO summit, but not all allies believe that U.S. tactical nuclear weapons must remain deployed in Europe. In Washington, officials see the rationale for keeping those weapons in Europe as driven far less by the requirements of deterrence than by the need to assure those allies who regard the weapons as a critical symbol of America’s commitment.

But that does not mean that the number of nuclear bombs must remain fixed in concrete. When I interviewed officials from NATO member states three years ago, those from Central European countries that favored keeping U.S. weapons in Europe saw nothing magical in the level of some two hundred nuclear bombs. Indeed, one official suggested that eighty to one hundred bombs would provide the political assurance that his government sought.

Asia poses a different situation. U.S. tactical nuclear weapons have not been deployed in the region—either ashore or on U.S. naval vessels—since the early 1990s. As Lowther and Hustus point out, the deployment of strategic bombers to Guam and patrols by submarines carrying SLBMs in the Pacific underscore that the U.S. nuclear umbrella continues to cover Japan and South Korea. Reducing the total size of the U.S. nuclear arsenal, however, would not require ending either practice.

Lowther and Hustus conclude by stating “as [nuclear] arsenals decrease, the deterrence problem becomes more complex in a non-linear fashion. That is why less is not just less, less is different.” That could well become true at some point, but only when the United States and Russia have made far more dramatic reductions in their nuclear force levels than they have to date. A fifty-percent cut from current levels would leave the two superpowers’ arsenals “less,” but not necessarily “different.”

Steven Pifer directs the Arms Control and Non-Proliferation Initiative at the Brookings Institution.