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.