If you want to understand this year’s election, a book published in 1970 turns out to be surprisingly useful. Both liberal and conservative analysts have recently cited its ideas, and the Harris and Trump campaigns have embraced its arguments in different ways.

The book’s title is “The Real Majority,” and it appeared during Richard Nixon’s first term. Its authors were two Democrats hoping to save their party from future defeats: Richard Scammon, who had run the Census Bureau under John F. Kennedy, and Ben Wattenberg, who’d been a speechwriter for Lyndon Johnson.

Scammon and Wattenberg believed that their fellow Democrats misunderstood the country’s electorate. The energy of the 1960s had led the party to imagine that the typical voter was young and highly educated. As a hypothetical example, the book described a 24-year-old political science instructor at Yale University. In reality, the authors wrote, the typical voter resembled a 47-year-old woman living in the suburbs of Dayton, Ohio, who didn’t have a college degree and whose husband worked as a machinist.

This Dayton voter wasn’t poor, but she struggled with rising inflation. She worried about crime, student protests and drug use, polls showed. She felt ambivalent about the Vietnam War. She was one of the “plain people,” as Scammon and Wattenberg put it, who had long voted Democratic but was uncomfortable with the party’s leftward shift — toward the views of that 24-year-old Yale instructor. Unless Democrats changed course, the authors wrote, “we may well see Republican presidents in the White House for a generation.”

The book was prophetic: Republicans won four of the next five presidential elections, including landslides by Nixon and Ronald Reagan.