Joe Biden for the first time on Saturday addressed criticism from Senator Bernie Sanders' campaign over the former vice president's record on Social Security. Biden criticized the Sanders campaign for pushing a video he describes as "doctored" that appears to show Biden agreeing with former Republican Speaker of the House Paul Ryan's stance on privatizing the social program. 

Speaking at a town hall in Indianola, Iowa, on Saturday, Biden fielded a question about his stance on Social Security from an audience member.

"Let's get the record straight. I'm not gonna blame anybody, but, well let me just say the facts: There's a little doctored video going around ... put out by one of Bernie's people ... saying that I agreed with Paul Ryan, the former vice presidential candidate, about wanting to privatize Social Security," Biden said.

Biden then noted that Politifact determined the video took his comments out of context and said his campaign will show the full video.

"It is simply a lie, that video that is going around," Biden also said. "And ask anybody in the press. It's a flat lie. They've acknowledged that. This is a doctored tape. And I think it's beneath him, and I'm looking for his campaign to come forward and disown it."

At issue is a video of Biden speaking at the Brookings Institution in April 2018 that's been widely shard by Sanders supporters and campaign staffers. The 20-second-long clip shows Biden apparently saying Ryan was "correct" about Social Security.

"Paul Ryan was correct. When he did the tax code, what's the first thing he decided we have to go after?" Social Security and Medicare," Biden says at the beginning of the clip. "Now, we need to do something about Social Security and Medicare. That's the only way you can find room to pay for it."

The Politifact article Biden cited on Saturday labeled the claim that he was agreeing with Ryan false. Biden's campaign said the former vice president was in fact mocking Ryan in those comments. 

The article also points to what Biden said after that 20-second clip, when he stated, "We need a pro-growth, progressive tax code that treats workers as job creators, as well, not just investors; that gets rid of unprotective loopholes like stepped-up basis; and it raises enough revenue to make sure that the Social Security and Medicare can stay."

It is worth noting that despite Biden's repeated use of the words "doctored" and "fake," the video is neither of those things. While the former vice president's comments were taken completely out of context and the Sanders campaign's framing of his words is misleading, the 20-second-video itself is real and unaltered.

The Sanders campaign online for weeks now has been prodding Biden into this fight over his record on Social Security, as they point to numerous videos as evidence the former Delaware senator was open to making cuts to the program in order to balance the federal budget.

"I tried with Senator Grassley back in the '80s to freeze all government spending, including Social Security — including everything!" Biden says dramatically on the Senate floor in a 1995 C-SPAN video.

Another video, shared recently by a Sanders campaign speechwriter, shows Biden on Meet the Press in 2008 while running for president saying he would "absolutely" look at ways to tinker with the costs of Social Security like raising the retirement age.

After Biden's campaign-trail response on Saturday, the Sanders campaign was quick to release a statement saying Biden should "stop trying to doctor his own public record of consistently and repeatedly trying to cut Social Security."   

"The facts are very clear: Biden not only pushed to cut Social Security — he is on tape proudly bragging about it on multiple occasions," Sanders campaign manager Faiz Shakir said in a statement.

The Sanders campaign has been making a concerted effort in the lead up to the Iowa caucuses to try to chip away at Biden's support among senior citizens. Nearly 40% of all Democratic voters over the age of 65 say Biden is their first choice, according to CBS News polling.   

Biden also took the opportunity on Saturday to lay out his proposal for Social Security.

"I have been a gigantic supporter of Social Security from the beginning," Biden said before breaking down his plan.

"What I'm proposing, and we'll get it done, is that everybody making over $400,000 will have to pay the same percentage you're paying if you're making $60,000," Biden said. Doing so, according to Biden will allow for larger to payouts to the "super elderly," prevent massive drops in payouts to someone whose spouse has died and make Social Security solvent for younger generations. 

Cara Korte contributed to this report.