A site called The Patriot Post created a meme called “They Lie” using two juxtaposed photographs. The first was a man looking at Mr. Trump waving to a sea of cheering fans; the second was a picture of that same man wearing glasses covered in the CNN logo, but seeing instead a group of Hitler Youth saluting their leader.

Townhall.com offered another provocative take: “How the Liberal Media Created Charlottesville.”

Mr. Trump and conservatives have pointed to several recent episodes as evidence of the left gone mad. They include the comedian Kathy Griffin’s posing for a picture with a fake severed Trump head, and a production of Shakespeare’s “Julius Caesar” that featured a Trump-like actor as the emperor who is fatally stabbed onstage.

Some seized on the shooting that seriously injured Representative Steve Scalise, Republican of Louisiana, at a congressional baseball team practice in June as further proof. One recent web video from the National Rifle Association accused liberals of attempting to “bully and terrorize the law abiding” as it implored Americans to “fight this violence of lies with the clenched fist of truth.”

But the tragedy in Charlottesville — specifically, the death of a young woman at the hands of a Nazi sympathizer who the authorities said ran her down with his car — undercut the notion that the black-masked radical leftists who smash windows and hurl firebombs are an equal menace.

Nor is it backed up by data on political violence. Of at least 372 murders that were committed by domestic extremists between 2007 and 2016, according to a study by the Anti-Defamation League, 74 percent were committed by right-wing extremists. Muslim extremists were responsible for 24 percent of those killings, and the small remainder were committed by left-wing extremists, the study concluded.

Noah Rothman, an editor for Commentary Magazine, a conservative opinion journal, said the emphasis for many conservatives is not on statistics that indicate who is the more violent offender. Rather, he said, the point is about the general tenor of political debate, which people like him believe is weighted against them.

“You don’t have a ton of reporters banging on the doors of Democrats asking them to denounce Antifa,” he said, referring to the militant Marxist-inspired group that rioted at Mr. Trump’s inauguration and often shows up looking for confrontation at sites where conservative writers like Ann Coulter and Milo Yiannopoulos are scheduled to speak.