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.