Optimistic and pessimistic arguments about nuclear proliferation were conceptualized decades ago. The best place to find them is in Scott Sagan and Kenneth Waltz’s The Spread of Nuclear Weapons: A Debate. Contrarian optimists like Waltz argued that proliferation will continue to happen slowly and in limited cases for good reason, since the bomb isn’t all that useful for conquest or war. Moreover, possession of the bomb by adversaries has reduced the likelihood of war. If proliferation pessimists were right, Waltz argued, many more states would possess the bomb and it would have been used in warfare.

Proliferation pessimists like Sagan counter that we have been fortunate to avoid battlefield use, but good fortune may run out, whether by command decision, breakdowns of command and control, or by accident. If more states acquire a bomb, pessimists argue, others will follow in their footsteps, and more can go wrong with additional bomb seekers. Moreover, the bomb hasn’t induced caution. While conventional warfare between nuclear-armed states has so far been avoided, border clashes haven’t and unconventional warfare has been fostered under the bomb’s shadow, as is most evident by Pakistan’s behavior.

The Waltz/Sagan debate didn’t anticipate the demise of U.S. bipartisanship and leadership on nonproliferation diplomacy, nor the “militarization” of Republican nonproliferation strategies, as defined by a heavy reliance on sanctions, opposition to less than idealized negotiated outcomes, threats to use force, and the use of force. Consequently, while nuclear nonproliferation remains a shared objective for Republicans and Democrats, deep fissures have opened with respect to the means to achieve desired ends. There are also serious divisions about how much U.S. effort is required for the proper upkeep of the Nonproliferation Treaty (NPT) “regime.” What do these trends suggest for proliferation optimism or pessimism?

To be sure, domestic U.S. divisions aren’t new—they date back to the rejection of the Comprehensive Test Ban Treaty’s ratification in 1999 by Senate Republicans, if not before. Subsequently, divisions have grown and are nowhere more evident than over the Iran nuclear deal. Supporters were surprised by how much the Obama administration and its co-negotiators managed to achieve, while opponents worry greatly over what the deal failed to accomplish. Support for the Iran deal has been nearly undetectable among Republicans on Capitol Hill, and Donald Trump seems intent to torpedo it.

Uncertainties about the future of proliferation now hinge on the Iranian and North Korean cases. Long gone are the halcyon years in the 1990s when nuclear-capable states (Argentina, Brazil) gave up their ambitions to become nuclear armed, and nuclear-armed states voluntarily gave up their home built (South Africa) or inherited (Ukraine, Belarus, Kazakhstan) stockpiles. There were diverse factors behind these extraordinary accomplishments; there was also an important common thread: all were accomplished without strong-armed tactics or the use of force. Instead, nonproliferation diplomacy was of paramount importance.

Michael Krepon is Co-Founder of the Stimson Center. This piece originally ran in The National Interest on March 29, 2018. You can read the full article here.