WASHINGTON – Former Vice President Joe Biden said Friday he anticipates some of Bernie Sanders' most vocal and controversial supporters will go negative as he and the Vermont senator battle for the Democratic presidential nomination.

"What we can’t let happen is let this primary become a negative bloodbath. I know I’m going to get a lot of suggestions on how to respond to what I suspect will be an increasingly negative campaign that the Bernie Brothers will run," he told the attendees of a Maryland fundraiser. "We can’t tear this party apart and reelect Trump. We have to keep our eyes on the ball, in my view."

It was that Biden referred to "Bernie Bros" as "Bernie brothers" during the call that got everyone's attention, including on Twitter, where a trending hashtag emerged Friday that was embraced both by Sanders' followers and those poking fun at Biden's phrasing.

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"You ain't ready for the Bernie Brothers," tweeted Sanders supporter and doctor Victoria Dooley.

Author and activist Leela Daou tweeted about her identity and the causes she supports and asked, "does that make me one of the #BernieBrothers?"

One Sanders supporter had fun with the wording of the remark, comparing it to the characters from the movie "Blues Brothers."

Another user compared the wording to the Mario Brothers, and another at the anachronistic wording.

Sanders campaign co-chair Nina Turner and national press secretary Briahna Joy Gray both retweeted posts from pro-Sanders Twitter users who had used the #BernieBrothers hashtag to show their support.

Sanders campaign spokesman Mike Casca told NBC News that Biden was "worried" about tweets while there were larger issues in the nation.

"Let's try to stay focused on the big issues," Casca said.

The Biden campaign's director of rapid response Andrew Bates replied to a reporter's tweet about the "Bernie Brothers" phrasing with an animation of Biden putting on sunglasses while "#DealWithIt" flashed on screen.

The former vice president's remarks about Sanders' supporters comes as some Democrats and one former presidential candidate, Sen. Elizabeth Warren, D-Mass., have expressed concern about the online conduct of Sanders supporters.

In a Thursday interview with MSNBC's Rachel Maddow, Warren condemned the "bullying" and "online nastiness" of Sanders' supporters, saying it was a particular problem with them.

She said presidential candidates were responsible for the actions of their supporters who do "dangerous, threatening things to other candidates."

Warren said she had not been the sole target, citing Sanders supporters' attacks on leaders of a union in Nevada, saying, "They actually published the phone numbers and home addresses of two women...and really put them in fear."

Sanders told Maddow Wednesday evening he was "aghast and disgusted" by his supporters' actions and has distanced himself from the vitriol online.

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During his call to the fundraiser, Biden also disclosed a big fundraising haul for his campaign — $22 million in five days. He told CNN anchor Anderson Cooper on Monday night his campaign had raised $33 million in all of February.

Sanders has built up a small-dollar fundraising advantage in the race so far, and Biden joked to his fundraiser's attendees, Sanders will "throw the dishwasher at me."

"We’re going to be OK," Biden said. "I just have to keep steady and moving forward and just laying out what we’re going to be talking about in a coherent way.”