Harvard University’s Graham Allison will discuss what he considers the imminent threat of nuclear terrorism on American soil in his talk, “Nuclear Terrorism: The Ultimate Preventable Catastrophe,” at the 16th annual Margolis Lecture at 5 p.m. on Monday, May 21 in Social Science Lecture Hall 100. A former advisor in the Department of Defense under presidents Ronald Reagan and Bill Clinton, Allison has the the unique distinction of twice having been awarded the Department of Defense’s highest civilian award. At Harvard, he founded the John F. Kennedy School of Government, which he developed from a small program into a major professional school of public policy and government.