Terrified by the prospect of others hearing the actual tapes, Nixon refused again, and instead made public “edited transcripts” of them.

The release of the transcripts became a fiasco for the president. Rather than helping the White House control the conversation, the documents became objects of cultural fascination. Newspapers printed them in full as special sections; radio stations broadcast live readings of them; the paperback edition of the transcripts was wildly popular. A prudish White House transcriber had replaced many four-letter words with “expletive deleted,” which became a popular catchphrase.

Moreover, Congress checked the actual tapes against the transcripts and discovered that someone had edited them in ways that benefited Nixon. For example, one conversation from March 22, 1973, recorded the president telling his aides, “I want you all to stonewall it, let them plead the Fifth Amendment, cover up, or anything else” — a vivid passage mysteriously absent from the White House transcript.

The discrepancies between the White House transcripts and the tapes became evidence of further malfeasance. When the Supreme Court ruled that he had to turn over more tapes, including one in which he explicitly directed the Watergate cover-up, Nixon resigned.

Nixon did everything he could to prevent Americans from hearing how he sounded in private . Later, he said that his chief mistake in Watergate was not abuse of power, but rather his failure to conceal evidence. “If the tapes had been destroyed,” he told the journalist David Frost, “I believe that it is likely that I would not have had to go through the agony of resignation.” Nixon realized that the tapes had bared his true self to the public — and thus cost him the presidency.

To be sure, Mr. Trump is no stranger to cover-ups. He hides his tax returns and refuses to discuss his businesses. But in the case of the Ukraine phone call, where there is documentation that he asked a foreign leader to interfere in an American election, he insists he has no regrets. His unorthodox conversations, the president insists, are “perfect.” He dares his opponents to find fault with what he presents as his routine conduct of foreign affairs.

Nixon’s opponents needed to produce evidence that revealed the real Nixon. The president’s critics today have a greater challenge: to persuade enough voters that the real Mr. Trump — whom we already know — is a criminal worth removing from office.