To be Jewish and European today is to wonder just who can be trusted. If you're one of the 1.5 million Jews of Europe, you're still coming to terms with the string of shocking terrorist attacks on Jewish primary schools, museums and markets over the past five years; many have come to distrust their Muslim neighbours.

Yet there's a growing sense now that, as terrifying as this threat is, it may be the lesser of their worries. This year's dramatic political shifts have led many to worry about a far larger, non-minority group, a surprising number of whom seem to be returning to anti-democratic, anti-minority politics aimed at Jewish populations.

Until recently, far more attention was focused on the first threat. That's because the far-right parties, such as France's National Front, Britain's UKIP and the Alternative for Germany, have in recent years tried to gain mainstream democratic credibility by attempting to kick out their overtly anti-Semitic officials, claiming to be tolerant of Jews (in large part by opposing Muslims) and making supportive noises about Israel.

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The problem, though, is that citizens who support these parties have not all gone along on this symbolic ride. If Europe's far-right parties have stopped talking about "devious Jews" and instead use euphemisms such as "globalists" and "cosmopolitan elites," their supporters are translating it back. It has become acceptable for many to speak openly against Jews, Muslims and even democracy itself.

To understand this, it's worth following the work of Yascha Mounk, a Harvard University scholar. Mr. Mounk made headlines this week with a new study, co-authored with Roberto Stefan Foa at the University of Melbourne, which found that voters in most European countries and the United States are increasingly less likely to believe it is "essential" to live in a democracy. This effect is stronger among younger people and right-wing voters.

For Mr. Mounk, this is part of a larger phenomenon. Two years ago, he published Stranger in My Own Country, a memoir of his life as a young German Jew. It noted that the Christian Europeans around him, while professing liberal tolerance, were continuing to treat Jews such as himself as different, other or outside. In an essay titled "Europe's Jewish Problem," he linked these observations to the rise of the new right-wing populist movements.

"Europe's political climate is more hostile to Jews now than at any time since the second intifada," he wrote. But he concluded that it wasn't Muslim anti-Semitism leading the trend; rather, it was the far larger populations of Christians. As he noted, the number of Spanish citizens who express unfavourable views of Jews is almost 50 per cent; Muslims make up less than 3 per cent of Spain's population and aren't growing fast. So "a European anti-Semite remains far more likely to be Christian than Muslim."

The larger problem, he concluded, is "the tendency of wily politicians to play Jews and Muslims against each other for purposes of their own."

A recent large-scale survey of French attitudes toward Jews by political scientist Dominique Reynié found that anti-Semitism in general is declining, but the country's Muslims do indeed have higher rates of anti-Jewish beliefs than the general population. What really stood out, though, were the many people who support Marine Le Pen's National Front party: They were even more likely than Muslims to agree with Jewish-conspiracy claims such as "Jews use their status as victims of the Nazi genocide for their own interest" or "the Jews are responsible for the current economic crisis." And they were almost equally likely to support statements such as "there is a Zionist conspiracy on a global scale," at rates twice as high as the general population. Muslims make up only 7 per cent of the population of France, but Ms. Le Pen commands at least one-fifth of the population, and her support is rising fast.

These parties and movements, Mr. Mounk concluded, attract those who are hostile toward both Muslims and Jews. "The very same revival of nationalism that has been fuelled by their invocation of Jews [as foils for their politics]," he wrote, "can, in this way, quickly turn into anti-Semitism." And that, combined with a growing group of voters who don't care about democracy, is something that Europe ought to fear.