But there is one claimed identity that Democrats do not ­embrace: the white one. And victory in 2020 might run directly through the states where it could play a decisive role.

In 1964, after President Lyndon Johnson signed the Civil Rights Act, it’s said he turned to a key aide with an air of political resignation and lamented, “We have lost the South for a generation.” Johnson was right, though his analysis was too narrow. In fact, that year, he became the last Democrat to win the white vote nationally. Ever since, with the landmark legislation realigning the major political parties, race has increasingly become a tool, and indicator, of political persuasion.

To exploit racial resentments and capture white voters, Republicans dog-whistled away—sometimes shrilly, sometimes gently. Richard Nixon declared a “war on crime.” Ronald Reagan went after “welfare queens.” George H.W. Bush conjured the specter of African-American prisoner Willie Horton, who raped a white woman while on furlough. Democrats, in turn, pursued a series of measures, including tough sentencing laws, to prove themselves tough on crime and compete for the white vote. Hillary Clinton, in remarks many criticized for their racial overtones, famously spoke of young ­“superpredators” and the need “to bring them to heel.”

But Trump is unique in the scale and depth of his appeal to whiteness, his sustained racially charged campaign to “make America great again” unmatched in modern political history.

And before the 2016 election, few appreciated the magnitude of the audience for such a message. According to Ashley Jardina, a Duke political scientist who studies whites and American politics, at least 40 percent of Caucasians acknowledge having some degree of “white identity,” a loose term that exists on a spectrum. Racists who support hate groups like the Ku Klux Klan are a small minority of these so-called white identifiers, about 10 percent. The rest, she says, are usually more animated by political and economic forces. The common thread among white identifiers, she said, besides whiteness, is a sense of aggrievement.

“When we think of racial prejudice, we think of antipathy toward people of color, a general sense of animus,” Jardina says. “There is a subset of people in the U.S. who feel their white race is important to them and feel the demographics are changing and the privileges and advantages that they have are under attack. That is different from ‘I just don’t like black people.’” She acknowledges that there is a relationship, “but it’s not the same thing, although the consequences of these two attitudes might sometimes be the same.”