On April 22, Polish President Andrzej Duda made the latest in a series of pitches from Warsaw to host U.S. nuclear weapons in the NATO nation. Last June, Polish Prime Minister Mateusz Morawiecki made similar statements in reaction to Russia’s announced deployment of tactical nuclear weapons to its close ally Belarus, which borders Poland.

This call has been echoed in the U.S. as well. Voices from The Heritage Foundation and the American Enterprise Institute have joined in the chorus invoking a nuclear future for Poland. In a surprising move, Sweden’s Prime Minister Ulf Kristersson – NATO’s newest head of government – also voiced an openness to hosting U.S. nuclear weapons on his country’s soil if the need arose. As NATO leaders prepare to meet in Washington in July to commemorate the alliance’s 75th anniversary, the nuclear noise from NATO’s more easterly members will doubtlessly grow louder. With the U.S. preparing to station nuclear bombs in England for the first time since they were removed in 2008, there already seems to be a growing willingness to expand the alliance’s nuclear profile.

Currently, the U.S. stores some 100 nuclear weapons in five NATO countries – Germany, Belgium, the Netherlands, Italy and Turkey – through its “nuclear sharing” initiative. This is far from its peak of 7,000 during the Cold War but it still represents significant destructive potential. Through this arrangement, the U.S. retains total control over its nuclear weapons stationed in Europe (today, all of them are B61 gravity bombs) but in wartime these weapons can be authorized for use on select multirole fighter aircraft operated by allied countries. These are tactical or non-strategic weapons with a destructive capacity much lower than an intercontinental ballistic missile. It’s important to note that the decision to use these weapons is solely in Washington’s hands. Poland is now making a push to become the sixth NATO state to participate in this nuclear sharing initiative.

During the Cold War, basing U.S. nuclear weapons in Europe had a strategic rationale – to offset the advantage in conventional forces possessed by the Soviet Union and its Warsaw Pact allies. Today, that advantage has been reversed, especially as the war in Ukraine continues to tie down and degrade Russian conventional combat capacity.

There are, however, three good reasons for U.S. policymakers to resist calls to expand nuclear sharing.

First, and most crucially, basing nuclear weapons in Poland or any other ally close to Russia’s border would be dangerously escalatory. The move would be seen by Moscow as an aggressive disruption of the strategic balance on the European continent and would likely invite further escalation in kind. This has the makings of an escalatory spiral. Regardless of what one thinks of Russian President Vladimir Putin’s actions in Ukraine or his role in the deterioration of East-West relations, it’s his perceptions that matter when NATO positions nuclear forces on his frontier.

As previously stated, Russia already faces a conventional imbalance vis-à-vis NATO, which has led Russia to lean harder on its own nuclear inventory to offset its conventional shortcomings. Russia’s concern about the West’s growing willingness to ignore these escalation dynamics has also led to the ongoing Russian tactical nuclear weapons drills that have put Europe on edge. This is a clear signal from Moscow reminding NATO that Russia has red lines of its own. NATO’s leaders would be prudent to not overstep them needlessly.

Second, expanding nuclear sharing doesn’t strengthen allied security. If anything, it could imperil it. Nuclearizing air bases in Poland incentivizes Russian targeting of those bases – so-called “counterforce” targeting – which in turn would undermine NATO’s ability to control the escalation spiral in a crisis situation. In any event, NATO’s nuclear deterrent would not be made more credible than it already is with six nuclear sharing nations instead of five. NATO rests easy under the U.S. nuclear umbrella and for that reason Putin has never once attacked NATO territory despite the alliance’s continued resourcing of Ukraine’s war effort, which has inflicted nearly half-a-million Russian casualties. This is a resounding testament to the strength of NATO’s deterrent as it is. There’s no need to toughen it further when the potential escalatory costs are so high.

Third, there are logistical considerations, not least of which is the cost of revamping Polish air bases to house B61 nuclear bombs. Storage sites must be constructed and –  importantly – maintained continuously. Security measures would also need to be in place that meet the Pentagon’s standards. NATO’s most recent investment program in these bases cost a staggering $385 million as of fiscal year 2024. Nuclearizing Polish bases would add substantially to this figure. Additionally, select Polish F-16Cs and F-35As would need to undergo the proper conversion processes (along with pilot training) to be rated to carry nuclear weapons. This would be a costly, yearslong process that, as we have seen, would be needlessly escalatory while adding nothing to NATO’s already solid deterrent.

Expanding nuclear sharing isn’t worth the strategic and material costs. President Joe Biden should bear that in mind when NATO leaders convene next month.

Scott Strgacich is a research associate at Defense Priorities.