Forty summers ago, the Supreme Court forced President Richard M. Nixon to surrender several key tape recordings that he had secretly made of his conversations, which proved incontrovertibly that he had directed an illegal cover-up of the June 1972 Watergate burglary and other crimes. Nixon resigned two weeks later.

Americans quickly got to see transcripts of some of the most incriminating tapes, including those on which Nixon ordered aides to have the CIA lie to the FBI in order to thwart the Watergate investigation (June 23, 1972) and others on which he blithely volunteered to raise $1 million to keep the burglars from spilling the beans (March 21, 1973). But it wasn’t until 1996, after a lawsuit by professor Stanley Kutler of the University of Wisconsin and the liberal advocacy group Public Citizen, that the government began releasing the rest of the 3,700 hours of tapes that weren’t deemed Nixon’s private property. Kutler’s landmark 1997 book, “Abuse of Power: The New Nixon Tapes,” reprinted transcripts of many of these additional Watergate tapes.

Many — but not all...