"As Democrats, we can't launch dishonest attacks against fellow Democrats," the ad said. "Bernie's campaign is not telling the truth."

I've been fighting to protect — and expand — Social Security for my whole career. Any suggestion otherwise is just flat-out wrong. pic.twitter.com/KWIIJgFqGk — Joe Biden (Text Join to 30330) (@JoeBiden) January 22, 2020

In response, Sanders' campaign manager Faiz Shakir said in a statement: “Joe Biden just released the first negative ad of the 2020 Democratic primary, and let’s be clear about why: he’s trying to distort his decades-long record of proposing and voting for cuts to Social Security benefits for millions of people. Joe Biden is no defender of Social Security, and a negative ad won’t help him outrun his record.”

Sanders' team also released their own video highlighting a recording of Biden in 1995 advocating to freeze federal spending in Social Security, Medicare and Medicaid.

"Let’s be honest, Joe. One of us fought for decades to cut Social Security, and one of us didn’t. But don’t take it from me. Take it from you," Sanders tweeted.

But a Biden official countered: "In what world is a social media video with no money behind it, released to defend the Vice President's record from a slew of attacks, an attack ad?"

Let’s be honest, Joe. One of us fought for decades to cut Social Security, and one of us didn’t. But don’t take it from me. Take it from you. pic.twitter.com/qh7qb1Hmcl — Bernie Sanders (@BernieSanders) January 22, 2020

The growing tension between the two has already faced some major bumps in the past few days. Biden incorrectly accused Sanders on Saturday of issuing a "doctored" video to attack him on Social Security. Sanders' campaign did assert Biden had supported former House Speaker Paul Ryan for cuts to Medicare and Social Security (which was marked false by PolitiFact), but the video was not altered by the Sanders campaign.

Sanders also had to apologize to Biden for an op-ed written by a supporter and redistributed by his campaign that called Biden "corrupt." The op-ed by Zephyr Teachout, a progressive law professor, was published in The Guardian on Monday and included in Sanders' campaign newsletter.

“It is absolutely not my view that Joe Biden is corrupt in any way. And I’m sorry that that op-ed appeared,” Sanders later said. Biden thanked him for the apology afterward in a tweet.