Bernie Sanders may have apologized to Joe Biden for an op-ed a surrogate wrote calling Biden "corrupt," but the two are continuing to argue over their records on Social Security. Late Tuesday night, Sanders tweeted, "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."

He attached a video clip of then-Senator Biden on the Senate floor from 1995 making this statement:

"When I argued that we should freeze federal spending, I meant Social Security as well. I meant Medicare and Medicaid. I meant veterans' benefits. I meant every single solitary thing in the government. And I not only tried it once — I tried it twice. I tried it a third time, and I tried it a fourth time."

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The video Sanders tweeted seemed to come in response to a video released by the Biden campaign earlier in the evening, which argued that the former vice president has always looked to protect social security. The video also took direct aim at Sanders, saying that he had dishonestly misrepresented Biden's record.

Biden tweeted Tuesday night, "I've been fighting to protect — and expand — Social Security for my whole career. Any suggestion otherwise is just flat-out wrong." The tweet was accompanied by a video defending Biden, with op-ed headlines accusing Sanders of negative and dishonest attacks against Biden. "Bernie's campaign is not telling the truth," the video says, concluding, "Bernie's negative attacks won't change the truth: Joe Biden is still the strongest Democrat to beat Donald Trump."

Appearing on MSNBC's "Morning Joe" from Iowa Wednesday, Biden said he accepted Sanders' apology for calling him corrupt. Biden said of Sanders' comments about his record on Social Security that "at a minimum, it was taken out of context" and insisted he has always been a "significant supporter" of Social Security.

After the appearance, CBS News' Ed O'Keefe asked Biden why he said he had accepted Sanders' apology but continued to attack him. Biden turned around and mocked the question, "Why why why why why," he asked, tapping O'Keefe on the lapels, then smoothing them, he told O'Keefe, "You're getting nervous, man! Calm down! It's ok."

Biden then added, "He apologized for saying that I was corrupt. He didn't say anything about whether I was telling the truth or not about Social Security."

In 1995, Bill Clinton was president and trying to balance the federal budget. It was a time when a number of politicians — Republicans, along with centrist Democrats — thought it would be prudent to cut the nation's spending and secure the future of entitlement programs such as Medicare and Social Security. At the time, Biden was among the deficit hawks who agreed with that approach.

Now, even though Social Security's insolvency may be looming — it could only be able to pay 80% of the benefits due by 2035 — few politicians care to reckon with what they view as the toxic politics of tweaking entitlement spending. Medicare is in worse shape, staring at possible insolvency by 2026.

Biden is now pledging that he won't cut Social Security or Medicare if he's elected and in fact, he'd even increase benefits for some. According to his campaign website, Biden would provide a bigger benefit for the oldest Americans. Workers who spent 30 years of working would receive a benefit of at least 125% of the poverty level.

Despite the increasingly shaky status of Social Security's medium-term prospects, Sanders and Elizabeth Warren want to increase benefits for workers. Both have said they'd collect more taxes from the wealthy to pay for their expansion, raising the caps on payroll tax income that's subject to Social Security taxes.

The newly-tweeted video wasn't the first time in recent days that Sanders and his team have critiqued Biden's past remarks on Social Security funding. A few days ago, the Sanders campaign was pointing out a 2012 video that takes a Biden remark out of context and appears to show him agreeing with former Republican Speaker of the House Paul Ryan about privatizing the program. It didn't show the part of the footage that makes it clear that Biden was being sarcastic.

He accused the Sanders campaign of releasing "doctored" footage and asked Sanders to apologize.

On Sunday, Sanders told CBS News: "[Joe] is a decent person. He is a friend of mine. People like him. And we're not going to make personal attacks on Joe Biden but I think the record shows that Joe's history in the Senate and my history in Congress are very different."

Bo Erickson contributed to this report.