The report was careful not to suggest that the Trump campaign “supported or endorsed” the anti-Semitic attacks, but noted that many had been sent by his supporters.

But some of the targets said that by evoking hostility toward minorities, Mr. Trump’s campaign had inspired and emboldened white nationalists and others to engage in acts of digital aggression toward “others” — including Jews — and toward Jewish journalists in particular.

“The best analogy I can give is that the campaign turned over a rock and a lot of stuff began crawling out from under it,” said John Podhoretz, the editor of Commentary magazine. “There were these code words and dog whistles that let it appear that people who had been doing things in the shadows could now start marching forward.”

Many of them have marched directly onto Twitter, no doubt because of its unique place in the political conversation: as a popular site for journalists, but also one of Mr. Trump’s favorite modes of communication, and thus a gathering place for his supporters.

“What I worry about is that this portends something very dangerous for our democracy,” said Jonathan Greenblatt, the chief executive of the Anti-Defamation League. “This is not just about anti-Semitism directed against Jews. The bigger story is the threat to free speech and the threat to a free press.”

The report was also critical of Twitter for not deleting or at least suspending the accounts of the vast majority of the offenders. “We’re seeing in a very coordinated way this kind of hate, and what we are not seeing are the platforms — in this case, Twitter — stepping up and dealing with it,” Mr. Greenblatt said.