Conversations on those and other delicate issues can be both important and painful, but the reality of American life is that they are happening ever more rarely. Over the past several decades, the United States has become increasingly segregated by class, with college-educated people marrying, living and socializing apart from less-educated Americans. The result has been that Americans have lost touch with one another, sociologists say, and helps explain why each side is so baffled by the other.

“If you went to Thanksgiving dinner 50 years ago, you’d be very likely to have dinner with people from a different walk of life,” said Robert D. Putnam, a professor of public policy at Harvard and the author of “Our Kids,” an investigation of class divisions in America. “Today, there are far fewer people who are different from us around that table.”

For upper-middle-class families like his own, “every single person will have a college degree or currently be in college,” he said. “That class homogeneity was not true of my family a generation ago.”

As the cultural divide becomes deeper, fewer Americans cross it.

Misty Bastian, 61, an anthropologist at Franklin & Marshall College in Lancaster, Pa., is originally from rural Tennessee. Since serving in the Air Force in the 1970s, she has lived all over the world and earned her Ph.D., two milestones that have set her apart from most of her extended family.

She said that she had sensed a “parting of the political ways” from her family for a long time, but that her support for Hillary Clinton seemed to be “the last nail in the coffin.”

The other day, a cousin who had “Trump proclivities” put a post on Facebook that she described as “all about Trump triumphalism.”