Rioters destroyed stores owned by Jews and chanted anti-Semitic slogans in demonstrations in France that stretched over three weekends last month.
A synagogue in western Germany was attacked, and swastika graffiti defaced shops in a predominantly Jewish neighborhood in Rome.
All have fueled fears of rising Gaza-related anti-Semitism in Europe -- and the attacks evoke haunting memories like frames from an old horror movie.
We thought we had learned. All of us. Forever.
"Never again." Remember?
But that has turned out to be wrong.
For instance, the recent rallies in Paris and its surrounding suburbs contained three distinct -- and not necessarily consistent -- currents.
The first current is France's "old" left, which has long been sympathetic to the Palestinian cause and criticizes Israel for its settlements policy and occupation of Palestinian territory.
The second current is clearly anti-Semitic. These are the demonstrators who chanted slogans such as "Hitler was right" and "Death to Jews."
The third current represents the "new" Europe and is the most difficult to gauge. It includes young Muslim professionals -- stockbrokers and accountants -- who have committed themselves to France and its republican values. Many said they took part in their first demonstrations because they are angry at Israel's military action in Gaza.
"I'm wearing the kaffiyeh [traditional Mideast headscarf] that my parents brought back from Mecca in 1996," said recent high school graduate Wassila. "I am anything but a supporter of demonstrations," said Arafa, a 33-year-old construction supervisor. These were two of many who gave only their first names to French reporters.
This is the sophisticated younger Muslim generation, most of them children of immigrants from North Africa. Now some of them, and non-Muslim young professionals as well, are in the streets with slogans such as "Israel out of France" -- a political formulation, not an anti-Semitic one.
An anti-Semitic leader in French social networks is Dieudonné, a French actor and comedian who has been repeatedly convicted in French courts of anti-Semitic offenses. He talks of a community of "non-Jews of France" who must stop being "slaves" of Zionism. In one of his songs, he says it's not up to him to "choose between the Jews and the Nazis. I am neutral in that business."
It is a fluid, volatile moment for Europe -- and the world. European political leaders, who have occasionally been wobbly on Vladimir Putin's deadly antics in Ukraine, have been united and clear in denouncing anti-Semitism.
But there is a new generation of Europeans who will make up their own minds about Israel and its conflicts in Gaza. The group includes the young professionals who demonstrated against Israel and a broader group of young voters who are impatient with traditional European Union politics and bureaucracy. How will they react to posters such as those slapped up on stores owned by Jews in Rome saying "Jews -- your days are numbered" and "Anne Frank is a liar"?
Will this new generation -- for most of whom World War II and the Holocaust are chapters in history books -- reject the resurgence of anti-Semitism in Europe and condemn it to wither and die. Or will its members equivocate, and let prejudice pass as part of public expression -- unwittingly creating the soil in which this poisonous weed may grow, again?