Despite the focus on the dramatic political change taking place in the Middle East, Tehran’s barely hidden drive toward nuclear weapons remains justifiably high on the international agenda. Iran’s nuclear efforts and lack of cooperation with IAEA inspectors have led to international and unilateral sanctions, innumerable diplomatic discussions, and a near-constant flow of op-eds. Much of the debate, however, has examined Iran’s nuclear potential in binary terms; either Iran will have nuclear weapons or it won’t.The manufacture and deployment of a nuclear weapon (”unacceptable,” according to President Obama) would be an obvious violation of Iran’s obligations under the Nuclear Non-proliferation Treaty (NPT), and would subject the country to harsher punitive measures than it currently faces.Abandoning its nuclear weapons efforts, though decreasingly likely, would include cessation of Iran’s entirely superfluous uranium enrichment activities and compliance with the transparency requirements of the NPT.Rarely raised is a third possibility: that Iran will pursue the “Japanese option” of becoming and remaining a nuclear threshold state. Japan is widely acknowledged to have both the technological ability and the stockpile of plutonium (the by-product of its peaceful nuclear energy generation) required to produce over 1,000 nuclear weapons (by comparison, China is estimated to have around 175). The saying goes that Japan is just a “screw-turn” away from being a nuclear armed state, but for historical, ideological and political reasons, as well as because of its comprehensive defense agreement with the United States, it has chosen not to turn the screw. Japan thus remains comfortably at the nuclear threshold, enjoying the legitimacy conferred by nuclear transparency, while knowing that, if needed, nuclear weapons are well within reach.Iran, though currently far from transparent, and with a record of nuclear obfuscation, might be pursuing a technically similar path, opening some of its facilities to observers, while developing the technology and infrastructure needed to field and deliver nuclear weapons within months, but not planning to take that last step. The threshold is not a single point; depending on a state’s progress to date, it includes a variety of activities that could be completed in anywhere from days to months. Regardless of whether Iran is at the threshold, a nuclear weapon could be little more than a decision away.IN SOME ways the nebulousness inherent in Iran remaining a threshold state threatens to put the US as well as its Middle Eastern allies in a tougher spot than would be the case if Iran unmistakably developed nuclear weapons. Such a situation could nevertheless strengthen domestic support for and enhance the regional and international prestige of the Iranian regime, making efforts to influence or undermine it more difficult.Iran could exploit its posture by pairing diplomatic demands with explicit or implied threats that it will cross the threshold. Avoiding this outcome is likely to cost the international community dearly in political, economic, and other terms. The much-feared prospect would likely result in a constellation of nuclear threshold states. It also would be more difficult to build diplomatic support for further sanctions against an Iran thought to have ”responded” to previous pressure by stopping just short of developing nuclear weapons. Iran therefore could glean many of the strategic benefits of nuclear weapons without actually having them.One could argue that Iran’s nuclear development program has already made it a threshold state. However, an Iranian decision to remain so for an extended period is likely to introduce increasing uncertainty to an already unpredictable region, which could be dangerously destabilizing. To avoid strategic surprise, states might feel increasingly compelled to invest intelligence and early-warning resources toward understanding where Iran is, as Saudi Arabia might be doing. As uncertainty rises, these states might become decreasingly willing to take chances. Though Iran undoubtedly sees deterrence value in its nuclear efforts, lingering at the threshold could make ostensibly pre-emptive war more, rather than less, likely.IF BEING a threshold state is so treacherous, why is Japan’s threshold status tolerated? Because Japan is fully compliant with its NPT obligations, its facilities are regularly and fully inspected by the IAEA, and it is governed by a democracy accountable to its citizens, its allies and the international community.Iran’s nuclear efforts, whether intended to produce a bomb or to stop short of doing so, would be far less ominous and arouse far less suspicion and opposition if the country’s regime did not have a well-deserved reputation for menacing neighbors, financing and equipping terrorist groups, and brutally suppressing internal opponents.Given the dangers posed by Iran as a threshold state and its record of NPT violation, it is essential to ask if the US administration’s and its allies’ current approach is sufficient. A more comprehensive stance would broaden its scope to define explicitly and consistently what these states’ red lines are, and what the penalties will be for crossing them, and ensure that these messages are unambiguously conveyed to Tehran.The consequences of too little, too late, might prove catastrophic.While the United States, Israel, Saudi Arabia and other Middle Eastern states might not agree completely about the threat posed by Iran as a nuclear threshold state, all can agree that the uncertainty is itself threatening, more so every day.The writers are research fellows at the Institute for National Security Studies, Tel Aviv University.