On balance, the United States’ nonproliferation efforts have been remarkably successful. No country that does not already have nuclear weapons seems to be developing them, although some, such as Iran, have the capabilities to do so. Most countries have opted not to build their own warheads in part because international treaties have erected legal, political, and normative barriers to the bomb and in part because the United States has made extensive security commitments to its allies around the world. Washington and its partners have also established that those who get caught proliferating face tough penalities.

But although nuclear proliferation has remained mostly in check so far, there is reason to doubt whether it will do so indefinitely. The international order and the United States’ role within it are changing. The treaties, security commitments, and sources of leverage on which nonproliferation rests may not survive these shifts. Washington shouldn’t be surprised if the nuclear landscape–and its ability to manage it–soon changes for the worse.

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