The United States will deploy a national missile defence (NMD) system within the next decade. The question is no longer, therefore, whether to build an NMD system, but how to do so without making the US less secure. Washington must avoid two risks. One is that Moscow will respond by taking steps that raise the risk of nuclear war. The other is that the US Congress will reject a deal worked out with Moscow to modify the Anti-Ballistic Missile (ABM) Treaty to allow for NMD deployment. Avoiding these two risks requires astute diplomacy abroad and smart politics at home. On the international front, the US needs to move quickly to strike a deal with Russia on modifying the ABM Treaty. On the domestic front, the Clinton administration needs to act quickly to begin building domestic political support for any deal that it might reach with Russia.