Nor does it mean that anything like a majority of Sanders’s supporters support the nastiness carried out in his name. Yet no other Democratic candidate has so many venomous followers — no Biden Brothers or Warren Sisters to return fire with fire. The only real analog in U.S. politics today to the Bernie nasties are the Trump nasties. They resemble each other in ways neither side cares to admit.

The most obvious resemblance is the adulation they bestow on their respective champions, whom they treat less as normal politicians than as saviors who deserve uncritical and uncompromising support.

“Surrender to a leader is not a means to an end but a fulfillment,” the philosopher Eric Hoffer observed in “The True Believer,” a book that remains as relevant in our populist era as it was in the totalitarian one. “Whither they are led is of secondary importance.”

Since it’s the usual destiny of saviors to be persecuted before they’re exalted, the response of their followers often is to persecute back. But persecute whom? In the demonology of most mass movements there is usually a near enemy and a far one, and the near enemy must be dealt with first and hardest. To this day, hard-core Trump supporters reserve their deepest spite for Republican NeverTrump holdouts (“human scum,” according to the president).

Just so with the Bernie Bros, who see more moderate Democrats not as kindred spirits or potential converts but as sellouts, even traitors — the proverbial enemy within. Partly this is about the normal competition for power, in which the show of ideological purity is treated as evidence of moral superiority.

But it also goes to the heart of what the Bernie Bros are really about. As they see it, ordinary civility isn’t a virtue. It’s a ruse by which those with power manipulate and marginalize those without. Democrats like Joe Biden who play by the rules of civility and bipartisanship aren’t just falling prey to the insidious manipulation. They are perpetrating and legitimizing it. No wonder nearly half of Sanders’s supporters won’t commit to or are unsure about voting for the Democratic nominee in the event it isn’t Bernie, according to a recent poll. Why bother voting for Oligarchy Lite?

If there is a silver lining here, it’s that the world has long experience with this brand of zealotry. Bernie Sanders may not be one of his own awful Bros, and may condemn their worst excesses. But there’s no reason to think they’ll lose their influence should he win the White House — just as Trump’s presidency has emboldened and empowered many of his own worst followers.

Is this the Democratic Party the Democrats want? They will cast their first votes for president on Monday evening at the party caucuses in Iowa. Now is the moment for second thoughts.

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