With the Iowa caucuses just over two weeks away, the Bernie Sanders campaign has been going after Joe Biden for his record on Social Security, claiming that the former vice president has supported cuts to the program.

Despite the claims, Biden still enjoys strong support among senior citizens: Nearly 40% of all Democratic voters age 65 and older say Biden is their first choice, according to CBS News polling. Senator Sanders on Sunday acknowledged Biden's support among seniors, but said it had more to do with personality than policy.

"Look, you know why? I'll tell you why. Because Joe is a nice guy. Okay? He is a decent person," said Sanders, in response to a question from CBS News about the former vice president's comfortable lead among seniors. "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."

WATCH: The @berniesanders campaign has long been critical of @JoeBiden's record on Social Security @CBSNews asks why Biden's senior support is so large despite Sanders criticism: Sanders: Look, you know why? I'll tell you why. Because Joe is a nice guy ... People like him pic.twitter.com/WRNhT2PCC1 — Cara Korte (@CaraKorte) January 19, 2020

The comments come after Sanders supporters and campaign staffers shared a video of Biden speaking at the Brookings Institution in April 2018. The 20-second-long clip shows Biden apparently saying former Republican Speaker of the House Paul Ryan was "correct" about Social Security. Ryan has supported changes to the program that include the addition of private accounts and raising the retirement age.

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The video takes Biden's remarks out of context, and Politifact said a claim by the Sanders campaign that Biden was agreeing with Ryan was "false." Sanders did however push back on Biden's characterization from Saturday that the video as "doctored."

"That's just not true," Sanders said. "I think all of the media who have looked at it, it was not doctored. It was what it is. The broader issue is not just one video, which, again I think all of the media who looked at it indicated it was not doctored. It is Joe's position on Social Security over the years versus my position on Social Security over the years."

Sanders on Sunday also said that he wasn't making a point about what Biden might do in the future, but taking a "legitimate" and "honest" look at Biden's record.

"I'm not saying anything about what Joe might do in the future, but I think it is important to know where a senator has come from and where his head is at, and Joe's record on that is a little different than mine," Sanders told CBS News after being asked directly if he believes Biden would make cuts to Social Security as president.

Biden on Saturday stressed that he is against cuts to Social Security, especially for those most in need. "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.