What to do about Iran's nuclear program is one of the most vexing foreign policy challenges confronting the Obama administration. This debate is increasingly characterized both by growing pessimism about whether the international community's diplomatic efforts and economic sanctions can prevent Iran from acquiring nuclear weapons and by guarded optimism that the consequences a nuclear-armed Iran are manageable. Writing in these pages last spring, James Lindsay and Ray Takeyh, both of the Council on Foreign Relations, maintained that the United States could contain Iran even if it developed a nuclear arsenal by establishing clear "redlines" that Tehran would not be allowed to cross without risking some type of retaliation. For example, if Iran used its nuclear weapons, transferred them to a third party, invaded its neighbors, or increased its support for terrorist groups such as Hamas and Hezbollah, the United States would be compelled to respond, although the measures it chose to adopt would not be specified in advance. This argument reflects the public position of many senior U.S. and European officials, as well as a number of prominent academics and defense intellectuals.
Yet this view is far too sanguine. Above all, it rests on the questionable assumptions that possessing nuclear weapons induces caution and restraint, that other nations in the Middle East would balance against Iran rather than bandwagon with it, that a nuclear-armed Iran would respect new redlines even though a conventionally armed Iran has failed to comply with similar warnings, and that further proliferation in the region could be avoided. It seems more likely that Iran would become increasingly aggressive once it acquired a nuclear capability, that the United States' allies in the Middle East would feel greatly threatened and so would increasingly accommodate Tehran, that the United States' ability to promote and defend its interests in the region would be diminished, and that further nuclear proliferation, with all the dangers that entails, would occur. The greatest concern in the near term would be that an unstable