Secretary of State John F. Kerry, left, before a negotiation session with Iranian Foreign Minister Mohammad Javad Zarif, right, in Lausanne, Switzerland, on March 20, 2015. (Brian Snyder/AFP/Getty Images)

This post is part of the “Iran and the Nuclear Deal” symposium.

If Iran and the P5+1 are ultimately able to reach a deal along the lines of the recent framework agreement concluded in Lausanne, will this reinforce or undercut U.S. nonproliferation policy? Unsurprisingly, advocates and opponents of the framework tend to disagree on this question. Advocates argue that a deal would reduce the odds of Iran acquiring nuclear weapons and therefore be a major nonproliferation achievement, while opponents argue that allowing Iran to maintain any enrichment capability leaves them too close to a bomb and contradicts the longstanding U.S. opposition to the spread of sensitive nuclear technologies.

Opponents are right to note that permitting Iran to maintain a significant enrichment capacity is contrary to U.S. nonproliferation policies. But this misses the point: Iran already has this capability, the United States has failed to prevent it despite its best efforts, and the question now is what to do about it. This is not the first time the United States has faced such a situation. Even after nonproliferation became a major priority in the mid-1960s, the United States has often found itself in a position where its most ambitious nonproliferation efforts have failed. More often than not, instead of using military force against the nuclear upstart or making unrealistic demands that the country surrender all of its nuclear capabilities, the U.S. government has elected to broker pragmatic deals to restrict a country’s nuclear program and thereby limit the damage to the nonproliferation regime.

As we document in a forthcoming article in International Security, after the United States tried and failed to prevent Israel, South Africa and Pakistan from acquiring the capability to construct nuclear weapons, they brokered deals to prevent nuclear tests, weaponization and/or public declaration of weapons capabilities. Some scholars and commentators have interpreted these deals as the United States making exceptions to its nonproliferation policy and/or looking the other way, much like opponents of the Iran nuclear deal argue today. Yet, these deals are a logical and pragmatic part of a functioning nonproliferation policy: Once the most ambitious objectives are no longer possible, a second-best alternative is sought. Put differently, nonproliferation policy does not stop when a country acquires the technical capability to construct a nuclear device, or even when a country has assembled a handful of bombs. A pragmatist would try to limit proliferation even after these milestones have been reached.

In particular, some U.S. policymakers have believed that preventing tests, weaponization and public declaration would lessen pressures for reactive proliferation or nuclear “domino effects” and thereby reinforce rather than undercut nonproliferation policy. Even after North Korea likely acquired its first significant amounts of fissile material in the early 1990s, the United States did not demand the immediate handover of existing stockpiles; it brokered an agreement in 1994 whereby North Korea agreed to freeze its program at its current status and eventually dismantle its facilities in exchange for light water reactors from the United States. In 2007 this was repeated when the agreement reached with Pyongyang did not include the country handing over its plutonium stockpile. While the deals with North Korea and Pakistan ultimately broke down, it is worth noting that in none of these cases – Israel, South Africa, Pakistan or North Korea – did a tipping point of nuclear acquisition occur following the deals with the United States.

What are the implications of this historical pattern for the current framework agreement with Iran? First, the United States is not – nor has it ever been – omnipotent in the realm of nonproliferation. It is not an almighty hegemon able to strong-arm all other actors to accept its conditions. Whether due to conflicting geopolitical priorities or a lack of leverage over nuclear aspirants, the United States has often been forced to come to terms with less than optimal nonproliferation outcomes. In these circumstances, U.S. policymakers have generally realized that “the perfect is the enemy of the good” and that pursuing unrealistic objectives makes less sense than reaching a reasonable compromise.

Second, the proposed deal with Iran is not exceptional. In this vein, it is instructive to note that the United States has permitted Japan, Germany, Brazil and other non-nuclear weapons states to maintain enrichment or reprocessing capabilities. The Treaty on the Non-Proliferation of Nuclear Weapons (NPT), as a legal instrument, allows member states to levitate on the threshold of nuclear weapons capabilities, and if anything, the deal with Iran is more restrictive than historical examples, not less.

Third, if history is any guide, a deal with Iran would not result in the proliferation cascades that are currently predicted by opponents of the deal. Limiting Iranian nuclear capabilities short of a bomb will most likely reduce the incentives for neighboring states to acquire nuclear weapons. Moreover, even if these states do consider going down the nuclear path, they will face strong opposition from the United States that will significantly complicate their endeavors.

Nick Miller is the Frank Stanton assistant professor of nuclear security and policy in the political science department and Watson Institute for International Studies at Brown University. Or Rabinowitz is a post-doctoral fellow at Tel Aviv University. She is the author of “Bargaining on Nuclear Tests: Washington and its Cold War Deals” (Oxford University Press, 2014).