Ms. Neumann now works for Moonshot, a private security company that tracks extremism online. Moonshot found a 51 percent increase in “civil war” references on the most active pages on 4Chan, the fringe online message board, in the week after Mr. Biden’s Sept. 1 speech.
But talk of political violence is not relegated to anonymous online forums.
At a Trump rally in Michigan on Saturday night, Representative Marjorie Taylor Greene, a Republican from Georgia, said that “Democrats want Republicans dead,” adding that “Joe Biden has declared every freedom-loving American an enemy of the state.” At a recent fund-raiser, Michael T. Flynn, who briefly served as Mr. Trump’s national security adviser, said that governors had the power to declare war and that “we’re probably going to see that.”
On Monday, federal prosecutors showed a jury in Washington an encrypted message that Stewart Rhodes, founder of the Oath Keepers armed extremist group, had sent his lieutenants two days after the 2020 presidential election: “We aren’t getting through this without a civil war.”
Experts say the steady patter of bellicose talk has helped normalize the expectation of political violence.
In late August, a poll of 1,500 adults by YouGov and The Economist found that 54 percent of respondents who identified as “strong Republicans” believed a civil war was at least somewhat likely in the next decade. Only about a third of all respondents felt such an event was unlikely. A similar survey conducted by the same groups two years ago found nearly three in five people feeling that a “civil war-like fracture in the U.S.” was either somewhat or very unlikely.
“What you’re seeing is a narrative that was limited to the fringe going into the mainstream,” said Robert Pape, a political science professor at the University of Chicago and founder of the Chicago Project on Security and Threats.
The institute’s researchers tracked tweets mentioning civil war before and after Mr. Trump announced the search on Mar-a-Lago. In the five preceding days, they logged an average of roughly 500 tweets an hour. That jumped to 6,000 in the first hour after Mr. Trump published a post on Truth Social on the afternoon of Aug. 8, saying “these are dark times for our Nation.” The pace peaked at 15,000 tweets an hour later that evening. A week later, it was still six times higher than the baseline, and the phrase was once again trending on Twitter at month’s end.