According to Colin Powell, national security advisor from 1987 to 1989, Reagan had been deeply affected by the 1951 film The Day the Earth Stood Still , in which space aliens warn earthlings that unless they stop settling their conflicts through war, the powers that be in the galaxy will destroy their planet.(During his presidency, Reagan repeatedly invoked the prospect of an alien invasion as a reason for the United States and the Soviet Union to overcome their differences. Whenever he did, Powell would mutter, "Here come the little green men.")
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For Reagan, who didn't draw a sharp contrast between reality and celluloid (he once told Israeli Prime Minister Yitzhak Shamir that he had visited Nazi concentration camps when in reality he had only seen them on film), the movies were chilling. Soon after viewing The Day After , Reagan attended a briefing on US military procedure in the event of a Soviet attack, as if the doomsday movies were playing out before him in real life.
http://www.foreignpolicy.com/articles/2010/06/07/think_again_ronald_reagan?page=0,2