The deadliest anti-Semitic attack in the history of the United States has shocked the world. In a social media post a few hours before the killing began, the shooter laid out his plan for all to see: "HIAS likes to bring invaders in that kill our people... I can't sit by and watch my people get slaughtered. Screw your optics, I'm going in."

HIAS stands for the Hebrew Immigration Aid Society, a group founded in the late 19th century in New York to help Jews escape pogroms in Russia and Eastern Europe. More recently, the group has focused its efforts on organizing members of the Jewish community to help protect undocumented immigrants.

To the man who apparently went in looking to "kill all Jews," HIAS appears to have represented the old conspiracy of the "treacherous" international Jew. It is the perfidious Jew who plans world domination through control of international finance, promotes speculation, controls the media and actively works to undermine the religious identity of Christian nations.

Anti-Semitic tropes' enduring power

The power of these anti-Semitic tropes, which have helped to justify the eradication of Jews through pogroms, concentration camps and mass killings, has not waned. The old Rothschild financier has been replaced by the billionaire George Soros. The rootless internationalism that Adolf Hitler denounced and associated with Jews is now the globalism that Steve Bannon and his alt-right contemporaries condemn.

A chorus of extreme American voices that has moved from the fringes to the mainstream has presented liberal Jews in the media, finance and government as powerful and dangerous. This strategy of demonization has now borne its poisonous fruit, and those who are intellectually responsible for this heinous attack are easy to identify.

Europeans be warned

Europeans need to recognize similar anti-Semitic signs at home. Hungarian Prime Minister Viktor Orban has pursued a plainly anti-Semitic electoral campaign that used Soros as the symbol of an anti-Hungarian globalist conspiracy. The leader of the far-right Alternative for Germany, Alexander Gauland, has vomited invective against the "globalized class" that supposedly occupies positions in academia, media, finances and NGOs. The British euroskeptic politician Nigel Farage, echoing Henry Ford's warning against the international Jew, recently told Fox News that George Soros was the "biggest danger to the entire Western world."

Meanwhile, Italy's far-right interior minister, Matteo Salvini, has railed against a financier whom he accused of wanting to "fill Italy with migrant slaves" and bringing about the financial ruin of Italy. And, much like the Pittsburgh suspect's charge against HIAS, Farage, Salvini, Orban and others have accused Soros and his network of NGOs of financing the migrant invasion of Europe.

These politicians are using arguments and language furnished from the darkest parts of our political inheritance for the sake of political expediency. Europe must shake itself out of the stupor and complacency into which it has fallen in the aftermath of this attack. We Europeans have a unique responsibility, one predicated on the blood that has soaked this continent's soil, to avoid this kind of atrocity in Budapest, Dresden or Warsaw. The time to act is now.