Experts point to several reasons. The volume and sheer ubiquity of information about politics, combined with Americans’ ability to instantaneously render public judgment on one another’s views, has made the political conversation much noisier. And for the first time the country is led by someone who inflames that conversation on a nearly daily basis, taunting his adversaries on Twitter and quickly triggering tens of thousands of responses.

“There is a constant obsession with the ups and downs, the tweets, who we’re supposed to be mad at — and that is different,” said the historian Jon Meacham, who has written a new book, “The Soul of America,” on how the country endured its most traumatic moments, from the Civil War to the rise of the Ku Klux Klan to Vietnam. “Trump has raised the metabolism of division to remarkable levels.”

Partisan identification is now a bigger wedge between Americans than race, gender, religion or level of education. The Pew Research Center, which for two decades has tracked demographic and partisan differences on issues like national security, immigration and the government’s role in helping the disadvantaged, found last year for the first time that the gap between Republicans and Democrats dwarfed gaps between people of different races, genders, religions and education levels.

There is a sense, especially among Democrats who recoil at Mr. Trump’s style of politics, that partisan affiliation reflects more than just a voting preference. Rather, it says something about your character. And where you come down on Mr. Trump is increasingly a decisive factor in whether or not someone wants to associate with you.

Sixty percent of Republicans and 65 percent of Democrats interviewed by Pew in a separate survey in March said that people who feel differently than they do about how Mr. Trump is handling his job probably do not share their values and goals.

Savannah Fehling, 23, of Sarasota, Fla., is one of many Americans whose own troubles live out the data. She said her relationship fell apart after she and her ex-boyfriend came to realize that their political differences — initially something that drew them together — were driving them apart. She described herself as “quite liberal” and him as “quite conservative.”