Mark Felt was the man behind the Watergate scandal, not Woodward and Bernstein.

Mark felt, at least in his own mind, had appointed himself as J. Edgar Hoover's successor.

Nixon, rightly so, considered Felt to be a "loose cannon" and planned to pass him over in favor of a more honorable man. Felt saw nothing wrong with warrantless wiretaps, "black bag jobs" and secret the files Hoover kept in order to threaten and manipulate politicians. Felt would have carried on "business as usual" which Nixon did not want, so Felt took Nixon down.