Technology
It is widely disputed whether the NMD concept is feasible [1].
Key equipment
Politics
Skeptics named the U.S. missile defense program of the 1980s "Star Wars" (after the hit movie series), since it seemed to its critics to be a mere science fiction scheme with no hope of success. It has since then gained the support of some of its erstwhile critics.
See also, Nuclear war, Nuclear weapon, Civil defense