This year marks the 50th anniversary of the presidency of Richard N. Nixon's Watergate Scandal. Following is an excerpt taken from the introduction of Daniel S. Chard's Nixon's War at Home: The FBI, Leftist Guerrillas, and the Origins of Counterterrorism, which shows how America's war with domestic guerrillas prompted a host of new policing measures as the FBI revived illegal spy techniques previously used against communists in the name of fighting terrorism. These efforts did little to stop the guerrillas—instead, they led to a bureaucratic struggle between the Nixon administration and the FBI that fueled...