That would deter any rational leader. Putin also sensibly proposes pooling American and Russian diplomacy, intelligence-gathering and military clout to thwart nuclear outlaws. India, Pakistan, Israel and North Korea all acquired The Bomb in part because the world failed to dissuade them. Rogues can be contained. South Africa and others have voluntarily dismantled weapons.
History offers alternatives to missile defence.
America's allies can only hope the Bush administration will discover them.