Donald J. Trump campaigned on the slogan “Make America Great Again,” a phrase whose “great” was widely heard as “white.” Certainly the election has been analyzed as a victory for white Christian Americans, especially men. Against Mr. Trump were all the rest of us: professionals with advanced degrees and the multiracial, multiethnic millions.

Though white Americans differed sharply on their preferences for president, the election of 2016 marked a turning point in white identity. Thanks to the success of “Make America Great Again” as a call for a return to the times when white people ruled, and thanks to the widespread analysis of voters’ preferences in racial terms, white identity became marked as a racial identity. From being individuals expressing individual preferences in life and politics, the Trump era stamps white Americans with race: white race.

I don’t mean that Americans suddenly started counting people as “white.” This has been going on since the first federal census of 1790, which enumerated three categories of white people (“Free white Males of sixteen years and upwards, including heads of families,” “Free white Males under sixteen years” and “Free white Females”). That census also tabulated two other categories: “All other free persons” and “Slaves.” Period. Black was not marked. Since 1790, population statistics have faithfully recognized a category of “white” people, sometimes more than one, especially native- and nonnative born. So I don’t mean that Americans suddenly discovered the category of white in 2016.

I’m saying that what it means to see yourself as white has fundamentally changed, from unmarked default to racially marked, a change now widely visible: from of course being president and of course being beauty queen and of course being the cute young people selling things in ads to having to make space for other, nonwhite people to fill those roles.

We have been seeing this change in popular culture and in higher education over the course of the last decades. Black and brown and Asian people sell you financial instruments and clothing. The president and first lady are black. Your college literature course includes Toni Morrison and Junot Díaz. But if you haven’t gone to college, where multiculturalism has been making its way for a generation, and if your version of America was formed in school in the 20th century, and that 20th-century image remains in your consciousness, you may have a lot to lose.  ...