One of the many problems Bernie Sanders will have to deal with over the next few months of campaigning is the zealotry of his own supporters. Today CNN published a story suggesting Sanders followers are uniquely aggressive online often bullying those who fail to fall in line. It’s titled “The ‘swarm’: How a subset of Sanders supporters use hostile tactics to drown out critics.

More than a dozen social media users spoke to CNN about their experiences with bullying by Sanders supporters.

They described threats against family members, the creation of imposter accounts that resembled their own and what some described as being “swarmed,” where barrages of vitriol filled their Twitter feeds and inboxes for days after they posted something critical of Sanders.

“I had never experienced that level of aggression before,” said Patty Kasbek, a veterinary technician in Oklahoma who said she criticizes President Donald Trump on Twitter more than any other political figure but said she faced the most hostility after she accused Sanders of being misogynistic. She said she received messages such as “STFU” and “eat this” poop emoji, among other insults.

Two other targets said they were so tormented by the online attacks they faced following their public questioning or criticism of Sanders that they requested those specific circumstances not be reported for fear such harassment could start up again. Both said Sanders supporters exposed their addresses, shared their personal photos and spread information about their relatives and work colleagues.

Sanders had tried to discourage bullying tactics on a few occasions but critics note that Sanders also frequently strikes an angry pose online that amps up his followers:

In that tweet, Sanders is responding to someone who is a fellow Senator with an equivalent status. That seems like fair game. But Sanders followers like to gang up on people who don’t have much power and often take things way over the line. Less than two weeks ago the NY Times published a story about progressives who said their refusal to back Sanders was met with threats and letters sent to their homes:

Some progressive activists who declined to back Mr. Sanders have begun traveling with private security after incurring online harassment. Several well-known feminist writers said they had received death threats. A state party chairwoman changed her phone number. A Portland lawyer saw her business rating tumble on an online review site after tussling with Sanders supporters on Twitter…

For some perceived Sanders critics, there has been mail sent to home addresses — or the home addresses of relatives. The contents were unremarkable: news articles about the political perils of centrism. The message seemed clear: We know where you live.

And as I pointed out when I wrote about this story, even as Sanders discourages this, he has also talked about rewarding RoseAnn DeMoro with a cabinet position in his administration. DeMoro’s crusade for single-payer in California became so toxic that the entire Democratic Caucus wrote a letter telling her to stop bullying Democratic elected officials.

Here’s the part that CNN won’t say but which needs to be said: Sanders is a socialist and socialists have a long history of idealizing violent revolutionary struggle. That’s why you still have people on the left walking around in Che Guevara t-shirts and thinking out loud about the glories of the French Revolution. This is the ideological sandbox Bernie is playing in and his refusal to distance himself from some of his own past extremism is a signal to these people that they are welcome in his campaign. That’s how he winds up with folks like this working for him.