“These are not creative people,” said Dan Friedman, the executive editor.

Still, “to some staff members, it was a little terrifying,” Ms. Eisner said at the publication’s Financial District headquarters, several blocks from The Forward’s birthplace on the Lower East Side.

The threats were serious enough that Ms. Feddersen decided to add more security measures, including a third door that requires an ID to pass through before reaching the office. When threats are made, The Forward now has a set process on how to report them to the police and the F.B.I.; the whole staff has gone through emergency drills.

“We really took it seriously, and it wasn’t fun,” Ms. Feddersen said. “It was not why anybody gets into this business. But that comes with the job, so we kind of have to do it.”

It was especially jarring for The Forward’s roughly 25-person editorial staff of mostly young journalists, for whom anti-Semitism in the United States had been something on the fringes that could be easily ignored — a generation that, in Ms. Eisner’s words, “grew up in Obama’s America” and took inclusion as a given. But it can be jarring even for Ms. Eisner, 61, who recalled recently walking by a church around the corner from her home on the Upper West Side that rents space to a synagogue, and seeing swastikas drawn on it.

“I’m written about on neo-Nazi blogs. David Duke talks about me on his Twitter feed,” said Sam Kestenbaum, a reporter who focuses on anti-Semitism and the alt-right, the far-right fringe movement that advocates a range of racist positions. “I knew that individuals received email threats, and certainly I did.”

When he tried to interview Andrew Anglin, the founder of the neo-Nazi website Daily Stormer, Mr. Kestenbaum was told, “I don’t talk to Jews on the phone.” Mr. Kestenbaum emailed Mr. Anglin questions instead.

Mr. Kestenbaum has also written about the white nationalist Richard B. Spencer and tracked a group of Jews who embraced white nationalism.