Douglas Brinkley on the Nixon tapes, 40 years after resignation
8 August 2014 Last updated at 00:05 BST
Forty years ago, President Richard Nixon resigned - becoming the first American president to do so.
The key evidence against him in the Watergate scandal came from audio recordings that Nixon had made in secret starting in 1971.
Rice University historian Douglas Brinkley says previous presidents had used recording systems but Nixon's use of automatic, voice-activated recording was unprecedented.
Nixon believed the tapes would stand as a historical record to help shape his legacy as a great statesman and highlight his foreign policy achievements, especially in dealing with the Vietnam War, the Cold War, and the thawing of US relations with China, Brinkley says. Instead, the tapes led to his downfall.
Brinkley and fellow historian Luke Nichter have transcribed 3,700 hours of White House tapes in the new book The Nixon Tapes,
He tells the BBC what the recordings reveal about Richard Nixon as a president and as a person.
Produced by Ashley Semler and Franz Strasser; filmed by Maxine Collins
Photos courtesy Nixon Presidential Library