Domestic Counterintelligence involves law enforcement agencies such as the Federal Bureau of Investigation (FBI) using surveillance tools originally developed to target foreign spies to neutralize American political dissidents.
A good example of this is COINTELPRO-- short for Counterintelligence Program-- which was a FBI intelligence/counterintelligence program started during the Cold War with the purpose of disrupting the activities of the Communist Party of the United States. In the 1960s, it was expanded to include a number of other domestic groups, such as the Ku Klux Klan, the Socialist Workers Party, the Black Panther Party, and other political organizations.
(From: https://vault.fbi.gov/cointel-pro & https://www.aclu.org/other/more-about-fbi-spying)
Spying: Assessing U.S. Domestic Intelligence Since 9/11 by 
A Threat of the First Magnitude by First installment in a 2-part exploration of controversial FBI history-- COINTELPRO. Apr 2023.
