This deteriorating relationship is troubling because Turkey is a long-standing NATO ally. But even more worrisome are the nuclear weapons — about 50 B61 gravity bombs — that the United States stores at Incirlik Air Base in Turkey, less than 100 miles from the Syrian border. On Wednesday, Trump appeared to confirm the existence of these weapons in a startling break with past practice, but over the weekend, U.S. officials reportedly were considering plans to withdraw them.

Why does the U.S. have nuclear weapons in Turkey, and what would be the risks of withdrawing them? Here’s what you need to know:

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1. These weapons are relics of the Cold War.

The United States first deployed nuclear weapons on Turkish soil in 1959. President John F. Kennedy used them as bargaining chips to end the Cuban missile crisis in 1962, agreeing to withdraw nuclear-armed Jupiter missiles from Turkey in exchange for the removal of Soviet nuclear weapons in Cuba. But Washington has continued to deploy shorter-range tactical nuclear forces since then.

Why does the United States keep nuclear weapons on foreign soil, and how does this strategy advance American interests? Our research reveals that three main strategic drivers behind these deployments.

First, these deployments were once a way of coping with technological limitations. In the early days of the Cold War, before intercontinental ballistic missiles (ICBMs) and nuclear-armed submarines became the backbone of the U.S. arsenal, putting nuclear weapons in Europe expanded the U.S. ability to respond quickly to an enemy attack. Today, of course, most of the U.S. nuclear arsenal is carried by ballistic missiles — rather than long-range bombers — so most of the world is within range.

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Second, nuclear deployments serve as a warning to potential attackers. U.S. leaders during the Cold War believed that putting nuclear weapons in Europe would discourage a Soviet invasion, because Soviet leaders would be worried that a limited conflict would quickly turn nuclear. Even after the dissolution of the Soviet Union, Turkish military commanders argued that U.S. nuclear deployments served as a deterrent to aggression by regional rivals such as Iran.

Third, nuclear deployments are also intended to reassure allies — including Turkey. Reassurance is not only about managing intra-alliance relations, however — it can also be an important nonproliferation tool. By mitigating the security concerns of allies, U.S. nuclear deployments could prevent them from launching their own nuclear programs.

2. Nuclear deployments in Turkey bring the United States few benefits.

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U.S. nuclear forces in Europe may have served a function during the Cold War, but they are increasingly obsolete.

A recent study we conducted shows that the critical factor for preventing aggression against U.S. allies is a formal alliance relationship with the United States — not the presence of U.S. nuclear weapons. Indeed, our research found that global deployments of nuclear weapons made very little difference for deterrence even during the Cold War.

This makes sense, because the United States doesn’t need to forward-deploy its forces to place allies under its nuclear umbrella. American missiles and submarines give it the capability to hit any target in the world. What matters is the United States’ commitment to defend its partners with nuclear weapons if necessary — not where these nuclear forces are physically located.

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U.S. nuclear forces in Turkey might, however, contribute to reassurance and nonproliferation. Political scientist Dan Reiter, for instance, has shown how countries with foreign nuclear weapons on their soil are less likely to explore their own nuclear options. Still, most U.S. allies — including Japan and South Korea after the early 1990s — have remained nonnuclear even without U.S. nuclear forces in place.

3. There are potential dangers to keeping nuclear weapons in Turkey.

While the benefits of these deployments are modest, the risks are significant. Nuclear weapons on foreign soil could be vulnerable to theft or sabotage. When Greece and Turkey, two NATO allies, were on the brink of war in 1974 the United States had nuclear forces stationed in both countries. Worried about the safety and security of these weapons, Washington secretly removed its nuclear forces from Greece and disabled all of the weapons in Turkey.

The 2016 coup attempt against Turkish President Recep Tayyip Erdogan reignited concerns about U.S. nuclear weapons at Incirlik. As tensions escalate today, some analysts and U.S. officials continue to worry about the safety and security of the B61s in Turkey.

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4. Is there a downside to withdrawing the weapons?

Would pulling out the nuclear weapons now mean the end of the U.S.-Turkish alliance? This concern is legitimate, but recent research suggests that it is overstated. The United States has withdrawn nuclear forces from many allied countries: Britain, South Korea and others. In none of these cases did the withdrawals damage the overall alliance relationship, nor embolden adversaries.

There is also a security challenge with withdrawing the weapons in the short term. Removing them from their storage vaults during a period of intense hostility could invite an act of sabotage.

In the long term, the larger risk is that removing the weapons will prompt Turkey to try to acquire its own nuclear weapons. After all, Erdogan reportedly is exploring this option. But as relations with Turkey deteriorate, it is by no means certain that the presence of a few U.S. weapons will prevent this outcome. And there are other political and diplomatic tools for dissuading Turkey from venturing down the nuclear path if the United States pulls out its nuclear forces.

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Matthew Fuhrmann (@mcfuhrmann) is professor of political science at Texas A&M University.

Todd S. Sechser is the Pamela Feinour Edmonds and Franklin S. Edmonds Jr. Discovery Professor of Politics and Public Policy at the University of Virginia and Senior Fellow at the Miller Center of Public Affairs.