To many of the more than 100,000 Jews in Germany, the outburst of anti-Semitism since the conflict flared in Gaza has a troubling undertone and has stirred especially painful memories. The Central Council of Jews in Germany has received hundreds of calls from members asking whether they should pack their suitcases and leave the country.

“I have not heard that for many years,” said Dieter Graumann, the council president. “When calls for Jews to be gassed, burned and murdered are bawled on the streets of Germany, that no longer has anything to do with Israel’s politics and Gaza. It is the most abhorrent form of anti-Semitism.”

Academics who study anti-Semitism say the acceptance of disparaging remarks about Jews has become increasingly common in the educated middle class over the past two decades. Especially on social media, where hashtags such as #HitlerWasRight have appeared, there has been a significant jump in slurs against Jews…

“Violence always starts in the mind,” Ms. Schwarz-Friesel said. “Attacks like that on the synagogue in Wuppertal are not just pulled out of thin air.”