Few things are simple about antisemitism because few things are simple about Jews. We are a nation, a religion, a culture, an “other.” At various times, we’ve also been thought of, falsely, as a race, most malevolently by the Nazis. Antisemitism has expressed itself over the centuries as political opposition to Jews, religious hatred, cultural disdain, xenophobia or racism. It’s a shape-shifting virus that has adapted itself to the reigning prejudices of different eras. But a common thread linking one strain to another is that antisemitism typically takes the form of a conspiracy theory. Such as? Deicide, for starters —...