In King Richard (Knopf, May.), journalist Dobbs mines secret White House tapes to illuminate the Watergate scandal.

Why did Nixon tape incriminating conversations?

The tapes were private documents for writing his memoirs. Henry Kissinger, his national security advisor, was making records of his telephone calls, so Nixon wanted his own record to make sure that he got credit for foreign-policy initiatives that Kissinger might take credit for. He was pretty inept with technology, so [chief of staff] Robert Haldeman recommended a taping system that Nixon couldn’t turn on or off, which meant that he taped everything—even discussions of how to spread hush money to the Watergate burglary conspirators. That was the fatal flaw.

The book covers the first six months of 1973. Why was that period so telling?

I started at Nixon’s second inauguration: he thinks he’s left Watergate behind—even the Washington Post isn’t writing much about it—and he has a 70% approval rating. But then the plot starts to unravel. At the Watergate break-in trial, the defendants start revealing that they were led by people in the White House. That climate of suspicion spread to Nixon and his aides, and they’re all fighting with each other. The period unfolded like a Shakespearean tragedy, from hubris to crisis to catastrophe, and enveloped the president. That’s one reason why I called this book King Richard.

You hear many Nixons, many extremes of emotion and character. He’s a decisive strategic thinker, one of the great foreign-policy presidents. He also throws nervous breakdowns, he’s drunk, maudlin, lashing out at enemies. You hear him getting desperate as he tries to extricate himself from the mire of Watergate. Then sometimes his daughter Julie calls while he’s discussing Watergate, and his tone of voice changes from chewing people out to loving exchanges.

What do the tapes reveal about his relationships with aides?

At that level you’re surrounded by courtiers who tell you what you want to hear. Henry Kissinger was a practiced sycophant who knew how to get on Nixon’s right side. Haldeman is an interesting character. He’s not just a yes-man; you can hear him reining Nixon in, in a subtle, respectful way.

How does Nixon compare to Donald Trump?

Nixon is a much more serious and consequential character. He had significant foreign-policy achievements. He read widely. Although his willingness to pick fights helped bring his presidency down, he didn’t take it to the extreme that Trump has with the election challenges. Nixon respected the ground rules of American politics.