Excerpts from Books and Wikipedia
"The Senate had set up a committee to investigate the Watergate affair. It discovered that President Nixon possessed tape recordings that revealed his personal involvement. He refused to hand over the tapes and tried to prevent officials from being questioned, but John Dean, one of the President's counsel told what he knew and implicated two of Nixon's closest aids, John D. Ehrlichman and H.R. Haldeman. They attempted to deny their own and the president's involvement, but it became apparent that President Nixon had been lying." [Furtado: 1001 Days]