The current American election campaign is being touted as the most fraught in recent history. After arduous internal battles, the Republican and Democratic parties have finally nominated their candidates for the presidency of the United States – presenting the public with a choice between two unpopular and widely vilified candidates.This turn of events is disheartening, as it is causing many voters to claim they will shun the ballot box in November. Far more disturbing, however, is the societal genie it has let out of the bottle – open expressions of Jew-hatred across the political spectrum. Thanks to social media, it is neither necessary nor possible to sugarcoat or qualify the nature of the comments on Facebook and Twitter.Nor can the words of angry mobs defending their candidate of choice by attacking their opponents be interpreted as political criticism.The cat is out of the bag, and its name is anti-Semitism.First came the white supremacists calling to send Donald Trump’s critics – whether Jewish or only perceived as such – to the gas chambers and bemoaning the fact that “Hitler didn’t finish off the job.” And now there are the Black Lives Matter and Students for Justice in Palestine gangs, banishing “Zionist pigs” from the Middle East and American universities. Oh, and burning the Israeli flag outside the Democratic National Convention – to protest Hillary Clinton’s victory over contender Bernie Sanders, a Jew. The irony would be sweet if it weren’t so tragic.Meanwhile, as was revealed by the latest report released by the AMCHA Initiative – a watchdog organization that monitors anti-Semitism on US campuses – Jewish students are the group most targeted for systematic attack. According to the report, which bases its findings on the State Department’s definition of anti-Semitism, this phenomenon has sharply increased since last year alone. And the top institutions of higher learning at which Jews feel least safe are Columbia, Vassar and the University of Chicago — illustrious schools filled with Jewish students, academics, alumni and donors.As the late historian Robert Wistrich told me in an interview nearly a decade ago, “On the substantive issue of when criticism of Israel becomes anti-Semitic, I think that there are good criteria. Every rational person understands the difference between criticism and defamation. If you talk about an individual in a defamatory way, you’re going to the heart of his character, his essence. The same is true of countries.”Indeed, the kind of anti-Israel vitriol spewed on the Internet and chanted at rallies is unmistakably defamatory. And though extreme right-wingers are guilty of it, it is the Left that has given it a cloak of legitimacy and intellectual respectability.This marriage made in hell is producing the satanic progeny that, if not kept in check, will destroy the very fabric of the free society that has enabled it to rear its ugly head and thrive.“Anti-Semitism is a kind of barometer to Jews and to nations, both of what is wrong – because it is often a symptom of major pathologies in a given society – and a warning signal of catastrophes to come,” Wistrich said.The “canary in the coal mine” metaphor could not be more apt today. It is worthy of note in this context that American flags were torched alongside Israeli ones at the DNC in Philadelphia this week.In 2007, Wistrich explained that, for historical reasons, “anti-Semitism has been much less of a political force in the US than in Europe.” America, he asserted, “is exceptional; it’s an immigrant society in which there’s no established state religion.”Though acknowledging that the US had periods of “outspoken anti-Semitism in the 1930s and 1940s,” he said things “improved dramatically in the 1960s – the beginning of the Golden Age of American Jewry.”Are we witnessing the tarnishing or even demise of that age? Let us hope, for the world’s sake, that the answer is no. The writer is the managing editor of The Algemeiner.