The most pressing security concern facing the incoming Trump administration is the threat of nuclear proliferation cascades. The pursuit of nuclear weapons in unstable regions not only increases the risk of mirrored pursuits in non-nuclear neighbors but can lead to military re-posturing in nuclear powers and embolden newly armed states to behave aggressively.
Iran poses the greatest threat today of sparking such a proliferation cascade. It is surrounded by regional conflicts, with proximate proliferation risks (Saudi Arabia and Iraq), nuclear-armed rivals (Israel), and interests that are often directly at odds with Washington’s.