Wedge: The Secret War Between the FBI and CIA, a nonfiction book by American historian and policy analyst Mark Riebling, explores the conflict between U.S. domestic law enforcement and foreign intelligence.

Riebling argues that relations have always been tense, dating back to the relationship between the two giants of American intelligence—Director J. Edgar Hoover of the FBI and Director William Donovan of World War II's Office of Strategic Services (the forerunner of the CIA).

In World War II, President Roosevelt (at the demand of the British, including Ian Fleming), allowed the creation of a new intelligence agency, against the wishes of FBI director J. Edgar Hoover.

The FBI in contrast focused on the building of legal cases to be presented in the US court system, and the punishment of criminals, and demanded 'clean living' agents who would act in strict obedience to Hoover's dictates.

When the Warren Commission issued its conclusions on the murder in 1964, it concealed "indications of a Communist role" because of an interagency conflict over the bona fides of the Soviet defector Yuri Nosenko, who insisted that Moscow had nothing to do with the crime.

"[7] Emboldened by the knowledge that his personal relationship with Nixon was far warmer than that of Richard Helms, the Lyndon Johnson-appointed Director of Central Intelligence, Hoover proceeded to break off direct contact with the CIA.

As Riebling writes, the Nixon White House quietly encouraged the two agencies to encroach on each other's territory, and it established the notorious rump group known as the Plumbers, whose key operatives came from both the FBI and the CIA.

[7] Nixon's conspiratorial mind-set, combined with his wont to exploit the two agencies for his own political purposes, led naturally to the President's effort to enlist both in the Watergate cover-up, which was strenuously opposed by Helms.

"[7] In the epilogue to the paperback edition, Riebling argues that the Aldrich Ames and Robert Hanssen spy cases further soured relations, resulting in liaison problems that contributed to the intelligence failures of 9/11.