“For all these years, this is a group of people that’s been very bitter about the fact that they feel like they can’t speak,” said Sarah Sobieraj, a sociologist at Tufts. “It’s not just that their policies haven’t been popular.” And then Mr. Trump says similar things, with a powerful platform, without apology.

When norms of acceptable behavior and speech start to shift, it can disturb the shared beliefs, values and symbols that make up our culture. “It’s really all of those things that we’re watching right now — they’re all up for discussion,” Ms. Sobieraj said.

Far-right activists gathering in Boston over the weekend were outnumbered by thousands of counter-protesters seeking to show whose ideas constitute the fringe. Employers and community members have communicated the same over the last week, shaming and firing some of the men rallying in Charlottesville who’ve since been publicly identified.

As the president has equivocated on their views — some are “very fine people,” he said last week — less powerful but more numerous voices are trying to make clear that they disagree.

Social scientists know that political leaders and institutions play an essential role in establishing norms. The American Psychological Association began to shift people’s views in the 1970s when the group declared that homosexuality is not a mental illness. The United States military did the same with racial equality when it began to desegregate in the late 1940s.

Tali Mendelberg, a Princeton political scientist who has written about norms around racial equality, points to several forces that nudged the changing views. The urbanization of the country exposed more people to egalitarian cultural ideas, and the nonviolent tactics of the civil rights movement exposed Americans to the brutality of racism. Big wars, she added, have helped advance racial equality.

“When the country needs African-Americans, to fight in the trenches or power the factories, it tends to make more room for them in the American mosaic,” Ms. Mendelberg wrote in an email.