Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.) and former Vice President Joe Biden Joe BidenSenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE ramped up attacks on each other Tuesday night as part of an escalating battle over their records on Social Security.

Sanders has hammered his rival for the Democratic presidential nomination, arguing that he backed proposed cuts to Social Security during his years as a senator.

Biden said he was committed to not only maintaining but also strengthening the program and released an attack ad Tuesday dinging the Vermont Independent as “flat-out wrong.”

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“Democrats, we can’t launch dishonest attacks against fellow Democrats. We have to beat Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE,” says a narrator in the nearly minutelong clip. “Now Bernie’s campaign has unleashed a barrage of negative attacks on Joe Biden that even accused Joe Biden of supporting ... cuts to Social Security.”

“Bernie’s campaign is not telling the truth. Joe Biden has repeatedly voted to save Social Security,” the narrator adds. “Bernie’s negative attacks won’t change the truth: Joe Biden is still the strongest Democrat to beat Donald Trump.”

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

Sanders’s campaign fired back in a statement, suggesting Biden's “negative ad” was meant to muddy the waters over his record.

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“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,” Faiz Shakir, Sanders’s campaign manager, said in a statement.

Sanders, whose campaign is centered around expanding the country’s social safety net and bolstering programs such as Social Security, fired the first volley in the latest back-and-forth, releasing a selectively edited video suggesting that Biden advocated for cutting Social Security while he was in the Senate.

While Biden was open to reforms that would have cut the program to try to balance the budget, as were other moderate Democrats, his campaign maintains Sanders’s clip was misleading and that he was in fact mocking GOP talking points about cutting the program.

The Sanders campaign doubled down after its statement rebuking Biden’s ad, releasing a clip of its own featuring archived Senate footage of Biden discussing cuts to Social Security.

“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 with the video.

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 dispute is just one of multiple brawls among the top-tier primary candidates less than two weeks before the first nominating contest in Iowa.

Among the higher-profile feuds are the disagreement between Sanders and Sen. Elizabeth Warren Elizabeth WarrenBiden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon MORE (D-Mass.) over whether he told her a woman could not be elected president.

While Sanders and Biden show no signs of letting up over their Social Security dispute, the two did appear eager to lay to rest controversy over an op-ed by a Sanders campaign surrogate published in The Guardian that accused Biden of corruption.

"Biden has a big corruption problem and it makes him a weak candidate," Zephyr Teachout, a prominent progressive surrogate for Sanders and former New York gubernatorial candidate, wrote. "I know it seems crazy, but a lot of the voters we need — independents and people who might stay home — will look at Biden and Trump and say: 'They’re all dirty.'"

After the campaign initially circulated Teachout’s piece, staffers quickly took it down from its website, and Sanders apologized to Biden.

"It is absolutely not my view that Joe is corrupt in any way. And I'm sorry that that op-ed appeared," Sanders said.

“Thanks for acknowledging this, Bernie. These kinds of attacks have no place in this primary. Let’s all keep our focus on making Donald Trump a one-term president,” responded Biden.