In December 1974, just four months after Nixon’s resignation, New York Times reporter Seymour Hersh revealed the existence of a long-running CIA intelligence program targeting U.S. citizens, a direct violation of its charter. Hersh had, in part, sourced his information on the CIA’s own internal review, begun after it was revealed that two of the Watergate burglars had formerly worked for the CIA, and had been given assistance by the agency following the break-in. The review, informally known as the “family jewels” detailed a litany of illegal and inappropriate activities undertaken by the agency from the 1950s onwards.

While the CIA would not fully declassify most of the “family jewels” report until 2007, Congress swung into action. On January 27, 1975, a special 11-member investigative body was established to look into abuses of power by the nation’s intelligence agencies. Chaired by Democratic Senator Frank Church of Idaho, the Church committee called more than 800 witnesses over the course of nine months, including several former officials from both the FBI and CIA.

Most of the hearings were held behind closed doors to protect intelligence sources, but a few, carefully selected cases of misconduct were investigated in televised sessions. Among those were a CIA biological agents program, the FBI’s COINTELPRO (a wide-ranging counter-intelligence program targeting domestic groups as disparate as the KKK, the Communist Party and the Black Panthers) and a series of secret programs led by the National Security Agency known as Operation Shamrock and Project Minaret.

“Shamrock” was a three-decade long surveillance program in which the NSA gained access (without obtaining warrants) to the international telegram records of all three major telecommunication companies. Ostensibly created to obtain intelligence on foreign agents, the program had expanded to include surveillance of American citizens and was intercepting some 150,000 messages a month. Another warrantless program, “Minaret,” saw more than 5,900 foreigners added to NSA watch lists, and an additional 1,600 U.S. citizens (including Muhammad Ali, Martin Luther King Jr., and a number of notable anti-Vietnam War activists) targeted. The FBI was also accused of illegally monitoring more than 200,000 pieces of mail to obtain intelligence, again without obtaining a warrant.

Among the revelations (first revealed during the Watergate hearings) was the scope of the Nixon White House’s “Huston Plan,” named after the administration aide who drafted it, which called for additional, coordinated domestic spying on left-wing activists via burglary and electronic surveillance, and even proposed the creation of domestic detention camps that could house anti-war protestors. The plan was initially approved by President Nixon and by the directors of nearly all the intelligence agencies, and was only squashed after FBI Director J. Edgar Hoover opposed it.

In the wake of the findings of the Church Committee, Congress created permanent intelligence oversight committees in both the Senate and House. They also proposed the creation of the Foreign Service Intelligence Act. The bipartisan bill, which passed the House 246-128 and the Senate 95-1, was signed into law by President Jimmy Carter on October 25, 1978.

A key component of the act was the creation of the Foreign Intelligence Surveillance Court, a tribunal tasked with reviewing requests from law enforcement and intelligence agencies such as the FBI and National Security Agency seeking permission to undertake wiretap surveillance on any “foreign power or an agent of a foreign power” within the United States. The FISA court was initially comprised of seven federal district court judges (expanded to 11 judges in 2001), who are appointed by the Chief Justice of the United States and serve staggered, non-renewable terms of seven years. Details of warrant requests are not disclosed, only the number of requests that have been approved or denied. As of 2013 more than 34,000 such requests have been made, and only a dozen rejected (although the government has withdrawn some requests on their own). The court has been harshly criticized by many, including civil liberties advocates, who see it as a too acquiescent to government requests, functioning as a mere “rubber stamp.”

FISA has been significantly amended in the four decades since it went it effect. In the wake of the September 11, 2001, terror attacks the newly-signed USA Patriot Act expanded the duration of FISA surveillance orders, allowed authorities to share information placed before a grand jury with other federal agencies and, most critically (and controversially) permitted authorities to gather foreign intelligence information on both U.S. citizens and non-citizens.

The 2007 Protect America Act, passed in the wake of revelations of widespread warrantless wiretapping during the Bush administration, further amended FISA to remove requirements for a warrant for federal surveillance of both foreign intelligence targets outside the U.S. and anyone in the United States (including U.S. citizens) communicating with them and granted immunity to telecommunications companies who provided access to data to law enforcement agencies. Additional amendments were made by the by the FISA Amendments Act of 2008 and the 2015 USA Freedom Act, passed after the scandal surrounding NSA whistleblower Edward Snowden, which aimed to end the NSA’s bulk collection of U.S. telephone records and provide greater transparency in the work of the FISA court system.

For more information on one of the biggest scandals in U.S. history, tune-in to the 3-night special Watergate, premiering Friday, November 2 at 9/8c.