U.S. President George W. Bush announced in December, 2001, that the United States would withdraw officially from the ABM Treaty of 1972. The U.S. decision opened the door to legal deployment of national missile defenses (NMD) of the American homeland. Russian President Vladimir Putin did not approve of the U.S. decision. But Putin refused to make the U.S. departure from the Treaty a reason for derailing further arms control or future U.S.–Russian security cooperation on other issues, including anti-terrorism. Regardless of Putin’s reaction, the passing of the ABM Treaty regime opens the door to a period of political and military uncertainty in the relationship between Russia and the United States.1 It also reflects U.S. concerns about post-Cold War threats for which deterrence without defenses might not suffice.