March 1983 President Reagan termed the Soviet Union the "evil empire" and announced the Strategic Defense Initiative (SDI), a satellite-based defense system that would destroy incoming missiles and warheads in space. He called upon the scientific community "to give us the means of rendering these nuclear weapons impotent and obsolete." This was a dramatic change in U.S. nuclear policy because defense against ballistic missiles had not been part of U.S. defense programs for ten years. (A ballistic missile is shot into space and then reenters the atmosphere over its target.) SDI was to destroy incoming Soviet missiles by intercepting and destroying them with either laser beams or particle beams shot from satellites or from the ground. Dubbed Star Wars by the press, SDI quickly became controversial. SDI supporters argued that this near-perfect defense would make the United States safer and real arms control possible. Supporters believed that once the Soviets realized their nuclear weapons were obsolete, they'd be more willing to give them up. Opponents argued that the complex technology involved was far from foolproof and couldn't be tested before it was used. If it did work, critics contended, SDI would only protect the United States from ballistic missiles, not from bombers or low-flying cruise missiles. Furthermore, they believed SDI would make arms control less likely. The Soviets would respond by building more weapons to overwhelm SDI. Lastly, SDI critics said the initiative violated the 1972 ABM (anti-ballistic missile) Treaty with the Soviet Union. In the treaty--part of the Strategic Arms Limitation Talks I agreement--the United States and Soviet Union had agreed not to build a nationwide anti-ballistic missile system. In 1985, President Reagan's legal experts claimed to have found a loophole in the treaty which allowed unrestricted testing of the components of a ballistic missile defense system. This claim became an issue both within the United States and between the United States and Soviet Union.