His work has led some of his graduate students also to embark on FBI research. Two of his former PhD students include Kenneth O'Reilly (FBI and HUAC) and Christopher Gerard (FBI and the Senate Internal Security Subcommittee). Several of his master's students also studied the FBI with him while taking PhDs elsewhere: David Williams (PhD, University of New Hampshire) studied the early history of the FBI; Francis MacDonnell (PhD, Harvard University) studied the FBI and the Fifth Column; Douglas M. Charles (PhD, University of Edinburgh) studied the FBI and the anti-interventionist movement of 1939–45, and the FBI's Obscene File. Charles R. Gallagher, S.J. (Boston College) credits Theoharis with inspiring an integration of FBI and intelligence sources into the study of Vatican diplomatic relations.