U.S. President Barack Obama came into office promising to work toward a world free of nuclear weapons. Over the past several years, the United States has made uneven progress toward that goal. The nuclear agreement with Iran, if strictly implemented, will preclude an Iranian bomb and mitigate the risk of nuclear proliferation in the Middle East for at least the next 10–15 years. But North Korea continues to develop and test its nuclear capabilities, India and Pakistan show no signs of winding down their nuclear competition, and Russia and China have forged ahead with the modernization of their nuclear arsenals, with little prospect of either country agreeing to negotiate nuclear reductions any time soon. And in Europe, the risk of nuclear use, although low, may be increasing.

It would certainly not be low-hanging fruit, but ridding Europe of its Cold War nuclear legacy would be a good place for the next president to achieve early progress in making the world a safer place. U.S. tactical nuclear weapons on the continent and NATO’s plans to modernize and increase the capabilities of its nuclear systems may be increasing the risk of nuclear use and undermining NATO’s conventional defense capabilities. The United States needs to take bold action to rethink NATO’s nuclear deterrent in order to reduce the dangers and strengthen the alliance. Such moves could include a freeze on tactical nuclear modernization, a phased withdrawal of all U.S. nuclear weapons from Europe, and measures to adapt and strengthen NATO’s arrangements for nuclear cooperation and consultations to reassure allies.

The Russian nuclear threat to Europe is not new. Moscow has leaned on nuclear weapons ever since the collapse of the Soviet Union took down the Red Army and Russia’s defense industrial base. Nonetheless, until very recently, the risk of nuclear war in Europe—indeed the risk of any armed conflict between NATO and Russia—has been virtually nonexistent. Since Russia’s aggression against Ukraine in the spring of 2014, however, what is rightly perceived as increased nuclear-muscle flexing has rattled European nerves. Russian officials have issued nuclear threats against NATO countries; at the same time, Moscow has increased air patrols of nuclear-capable planes, conducted simulated military exercises with nuclear weapons, and continued to modernize its tactical nuclear weapons opposite NATO.

A Russian paratrooper descends to the ground during a training exercise in the village of Nikinci, west from Belgrade, November 14, 2014. Marko Djurica / Reuters There are signs, too, that Russia is officially changing its war-fighting doctrine in Europe to include the possibility of early use of limited nuclear strikes in order to bring conflicts to a halt on terms more favorable to Russia. This is a dangerous development—not so much because Russia is developing new capabilities, but because the deterioration in U.S.-Russian relations has increased the risk of an accident, mistake, or miscalculation that could trigger a conflict.

The United States' and NATO's tactical nuclear plans are not helping matters. The United States intends to spend billions of dollars over the next decade to upgrade its tactical nuclear bombs stored in Europe—and the United States’ European allies will need to allocate hundreds of millions of euros to improve the infrastructure supporting these weapons and associated dual-capable aircraft. The more modern U.S. nuclear warheads that will replace the estimated 160–200 U.S. nuclear bombs currently in Europe will be smaller and more accurate—and Russia is reportedly making similar improvements to its tactical arsenal. According to U.S. General James Cartwright, former commander of U.S. Strategic Forces and Vice-Chairman of the Joint Chiefs of Staff (JCS), these weapons will make limited nuclear strikes more conceivable.

It is unclear, moreover, whether NATO’s modernized tactical nuclear weapons would actually add to the alliance’s deterrence and defense posture. Over the past two decades, the military rationale for maintaining U.S. nuclear weapons in Europe has all but disappeared. Over five years ago, when Cartwright was the vice-chairman of the JCS, he declared that U.S. tactical nukes in Europe were redundant because they fulfilled no military function that was not already being met by U.S. strategic and conventional forces. Colin Powell, when he was chairman of the JCS in the early 1990s, supported elimination of tactical nuclear weapons, and in 2008, U.S. European Command ended its support for maintaining nuclear weapons in Europe. Few today within U.S. and allied militaries would question these judgments.

Helicopters fly during a NATO military exercise at the Birgi NATO airbase in Trapani, Italy 19, October 2015. Tony Gentile / Reuters The more vexing issue for the alliance is whether these weapons have any political and psychological value if they do not possess any military utility. NATO experts including former Pentagon officials Franklin Miller and Kori Schake continue to maintain that the weapons based in Europe are essential for reassuring allies of the United States’ security commitment. They also argue that basing them in several NATO countries is a valuable demonstration of the alliance’s principle of “equal risks, equal responsibilities.” It is important to preserve this principle. But reassurance and burden sharing might be better served if NATO spent more of its precious defense resources buying weapons and capabilities—such as improved C4ISR, strategic airlift, and heavy equipment for defense in Central and Eastern Europe and the Baltic states—that are relevant to the real threats the alliance faces today and will confront in the future. It isn't clear why allies would be reassured by investments in new nuclear warheads and infrastructure that offer no real increase in usable military capabilities and no added deterrence beyond what British, French, and U.S. strategic arms already provide. Nor is it clear why these allies would be reassured by more modern NATO tactical nuclear weapons that could actually lower the threshold of nuclear use on allied territory.

The alliance, after much internal debate, gave an important nod toward revising its nuclear posture earlier in the decade. In NATO’s 2010 Strategic Concept and its 2012 Deterrence and Defense Posture Review, the alliance left the doors open to further nuclear reductions and to other means of providing reassurance and preserving burden sharing that do not require basing U.S. nuclear weapons on NATO soil, such as more rotational deployments of U.S. strategic bombers to NATO bases. Very little has been done in the past few years, however, to move in these directions. In view of Europe’s deteriorating security environment, the United States needs to restore momentum to these efforts or at least prevent backsliding.

The United States and Russia can and should begin a new high-level dialogue on deterrence and security issues writ large, including on the impact of planned developments in strategic and tactical nuclear weapons, conventional forces, cyberweapons, and missile defenses. And nothing should be kept off the agenda, as U.S. officials have occasionally tried to do in the past with missile defenses and so-called prompt-strike conventional weapons. The alliance should also take two more immediate and meaningful steps: impose a freeze on its plans to deploy upgraded B61 bombs in Europe and announce its commitment to undertake a phased withdrawal of all U.S. nuclear weapons from the continent.

Polish and U.S soldiers look at a Patriot missile defense battery during join exercises at the military grounds in Sochaczew, near Warsaw, March 21, 2015. Franciszek Mazur / Reuters There will be resistance to these measures. Some defense and arms control experts will argue that NATO should only change its nuclear posture if Russia takes reciprocal action through a new treaty. For example, Miller, Schake, and former NATO Secretary General and British Defense Secretary George Robertson have argued for either parity between NATO and Russia (where Moscow agrees to reduce its tactical nuclear weapons to NATO’s level) or equal percentage reductions in a legally binding treaty. This is a recipe, however, for forcing NATO to continue spending money on anachronistic nuclear weapons with little gain in deterrence, while siphoning funds from much-needed conventional defense improvements. Moreover, pressing Russia to negotiate reductions in—and especially the elimination of—its roughly 2,000 tactical nuclear weapons is a fool’s errand. Moscow sees these weapons as a counter to what it perceives as NATO’s conventional superiority and China’s growing military capabilities, as well as a symbol of its great power status. Further, the total lack of trust in Russia’s relations with the West makes it very unlikely that Moscow would agree to legally binding transparency and other confidence-building measures for its tactical nuclear weapons programs anytime soon.

There will also be pushback within NATO. Some members of the alliance—Belgium, the Netherlands, Norway, Luxembourg, and Germany—would conceivably support nuclear risk reduction measures; however, others such as the Baltic countries, Poland, and other Eastern European members would oppose any changes in the alliance’s nuclear plans and posture. The key to bringing recalcitrant members on board is to demonstrate with concrete actions, such as the Pentagon’s new budget proposal to spend $3.4 billion in the fiscal year 2017 to bolster U.S. and NATO military capabilities in Central and Eastern European countries and the Baltic states, that greater and more sustained investments in conventional force improvements will make them safer; that allied strategic nuclear forces are and will remain the backbone of NATO’s strategic deterrent for as long as nuclear weapons exist; that NATO’s security and nuclear deterrent are not tied to the presence of nuclear bombs on alliance soil; and that both can be maintained through broader and more robust NATO involvement in nuclear cooperation, planning, and consulting arrangements.

To borrow from the Cold War lexicon of the great nuclear strategist Herman Kahn, Russia is re-conceptualizing the ladder of escalation from conventional to nuclear conflict. NATO’s agreement to abandon plans for tactical nuclear weapons’ modernization and to eventually remove its nuclear bombs from Europe could, over time and as part of a broader strategy to re-engage Moscow on all aspects of Euro-Atlantic security, influence Russia to climb back down that ladder. And it could immediately strengthen the alliance’s defense and deterrent posture against the full range of current and emerging threats. To remain a nuclear alliance, NATO does not need to spend billions of dollars to upgrade nuclear weapons and infrastructure that it does not need and that risk lowering the nuclear threshold in Europe. The Strategic Concept and the Deterrence and Defense Posture Review left the doors open to a safer, stronger, and more affordable NATO deterrent posture. It is important for alliance leaders to pry these doors apart a little more—or at least keep them from being shut—when they meet in July at the Warsaw NATO summit.