The 40th anniversary of the nuclear Nonproliferation Treaty finds the NPT more vulnerable--and more vital--than ever.

Today marks the fortieth birthday of the nuclear Nonproliferation Treaty, one of the most important pieces of paper the United States has signed in the last half century--and one of the most popular. Even Bush officials, who went on a treaty-killing spree during their first year in office, made an exception for the NPT.

Why wouldn’t they? The NPT is one of the best deals the United States has ever made: It allowed five countries (including the United States) to possess nuclear weapons, but banned the rest from ever developing them. Today, every country on the planet except for India, Israel, North Korea, and Pakistan is a member. While pressuring the nuclear states to disarm, the NPT’s most significant accomplishment has been to reassure non-nuclear states that they don’t need the bomb, and in the past four decades more countries have given up nuclear weapons programs than have started them. In hindsight, the NPT seems like a diplomatic no-brainer.

But in 1968, it wasn’t. Conservatives like Senator Barry Goldwater and right-wing organs like National Review railed against the NPT because it didn’t fit into their binary, us-versus-them view of U.S. foreign policy. Conservatives distrusted international entanglements, and they feared that participating in a global security compact would simply embroil the United States in the problems of others. More specifically, they saw the Cold War as a battle between good and evil, and not only did negotiating the NPT require talking directly with the Soviet Union, they feared the treaty would undercut the fight against communism by forbidding us from giving nuclear weapons to our allies.

The Johnson administration had considered these arguments but ultimately decided that the proliferation of nuclear weapons had changed the way the world operated, undermining a zero-sum worldview in which a gain for us was automatically a loss for our enemies and vice-versa. Whatever the ideological conflict between the United States and the Soviet Union, nuclear weapons had made security interdependent--not only between the superpowers, but among all nations. As a presidentially appointed commission reported, “the Soviet Union, because of its growing vulnerability to proliferation among its neighbors, probably shares with us a strong interest in preventing the further spread of nuclear weapons.”

The treaty, then, was more than just a good deal for the nuclear-weapons powers; it was a manifestation of a growing emphasis on collective security--like the United Nations, but more effective, because the United States and the Soviet Union were working with, and not against, each other despite their rivalry. It marked a different way of conducting international diplomacy.

Today, the debate over the NPT is as relevant as ever. For all its successes, right now the NPT is threatened by violators like Iran and North Korea, global proliferation networks like A.Q. Khan’s, and the rapid spread of nuclear technology, leading conservatives like Charles Krauthammer to declare that “the era of nonproliferation is over.” Alas, even though threats like proliferation--and terrorism and global warming--indisputably require cooperative efforts, conservatism has remained simplistic and Manichaean.

It’s this ideological shortcoming that has handicapped Bush’s foreign policy, including his failures vis-à-vis Iran. And while some may doubt McCain’s conservative bona fides, he too, like Bush and Goldwater, divides the world into good guys and bad guys--and refuses to deal with the latter. That means that he won’t negotiate with Iran; he has denigrated engagement with North Korea; and he wants to expel autocratic Russia from the G-8.

To be sure, McCain’s worldview is more sophisticated--or at least more complex--than that of sixties-era conservatives. In late May, he gave a speech acknowledging that “we cannot achieve our non-proliferation goals on our own,” and, unlike George W. Bush, he even embraced the NPT’s goal of eventual nuclear disarmament. But it is hard to see how he can rescue the treaty from its current troubles--and thereby use it to, say, keep other Middle Eastern countries from reacting to Iran’s uranium enrichment with nuclear programs of their own--if he is unwilling to talk to countries he finds unpalatable, let alone those that are genuinely evil. Instead, McCain has defined his version of multilateralism chiefly through a proposed “League of Democracies” that would, in theory, enable the United States to act abroad without engaging countries it doesn’t like.

But successful nonproliferation requires near-universal cooperation, if not consensus, and McCain’s attitude toward Russia alone would seem to preclude that. How does one combat proliferation while demonizing a country with influence over both Iran and North Korea? How does one prevent nuclear terrorism by undercutting the state whose tons of unsecured fissile material represent the most fertile source for nuclear terrorists? Combine these inconsistencies with McCain’s apparent opposition to the Comprehensive Test Ban Treaty--which many countries see as a test of whether the United States is serious about reducing its reliance on nuclear weapons--and it’s hard to see how, however sincere his desire, he could really strengthen the nonproliferation regime.

Only a president who supports smart treaties like the CTBT, approaches powers like Russia pragmatically and cooperatively, and, yes, proves willing to sit down with enemies will truly be able to reduce the nuclear threat to America. The era of nonproliferation is not over--just the worldview that stands in its way.

J. Peter Scoblic, executive editor of The New Republic, is the author of U.S. vs. Them: How a Half Century of Conservatism Has Undermined America’s Security.

By J. Peter Scoblic