Hours before Sunday night's Democratic presidential debate in Charleston, S.C., Sen. Bernie Sanders (I-Vt.) and former secretary of state Hillary Clinton mixed it up in back-to-back interviews on four of the five Sunday morning talk shows.

Speaking on CNN's "State of the Union," Clinton distanced herself from a Politico report that a super PAC aligned with her campaign planned to air television advertisements demanding that the 74-year-old senator release his medical records. 

"Well, I don't know anything about it, but I have released my medical records," Clinton told host Jake Tapper. "And I remember being asked frequently for me to do so. And, so, obviously that's, you know, something I will leave up to the Sanders campaign."

The Clinton super PAC, Correct the Record, disputed the Politico report Saturday and did not immediately air any such ads. But in an email to supporters Saturday evening, Sanders campaign manager Jeff Weaver assailed the potential ads as "one of the most desperate and vile attacks imaginable."

On Sunday's "State of the Union," Sanders sought to tie Correct the Record founder David Brock to Clinton, saying that he had raised "millions of dollars from very wealthy people and special interests" to support her campaign. 

"Second of all, of course we're going to release our medical records," he continued. "Thank God, I am very healthy. We will get our medical records out the same way that Secretary Clinton has gotten her records out. It is not a problem."

On several of the shows, Clinton criticized Sanders' support for a 2005 law providing immunity to gun manufacturers and retailers. Earlier in the campaign, Sanders defended his vote, but in recent months he has said he would revisit it if he could. On Saturday night, his campaign released a statement saying he would support its repeal.

"Well, I am pleased that Sen. Sanders has flip-flopped on legal immunity for gun makers and sellers," Clinton told CBS' John Dickerson on "Face the Nation" Sunday morning.

But the former secretary of state continued to question whether Sanders would support closing the so-called "Charleston loophole," which allows gun sales to go forward if the federal government fails to complete a background check within three days. Authorities have blamed the loophole for allowing Dylan Roof, the alleged gunman in last year's Emanuel AME Church shooting in Charleston, to buy a gun, despite his having a criminal record. 

"So, now I'm calling on him to also flip-flop in the right direction and sign on [to] the legislation to change the Charleston loophole," Clinton said. 

Responding on NBC's "Meet the Press," Sanders said he "believe[d] very strongly in an instant background check" and thought "we have to expand on it." But he did not specifically commit to a longer waiting period for gun purchasers. 

"We are willing to look at anything that makes sense that keeps guns out of the hands of people who should not have them," he said.

Sanders said he thought it would be a mistake to "politicize" the issue and accused the Clinton campaign of doing so. 

"I think the reason that the Clinton campaign is getting defensive is they see that we have the momentum," he said. "They see that the issues that we are talking about — a disappearing middle class, and almost all new income and wealth going to the top 1 percent, a corrupt campaign finance system where people like Secretary Clinton can raise millions of dollars through super PACs — those are kind of the issues that they don't want to discuss."

The candidates continued their weeklong debate over Sanders' proposal to enact a single-payer health care system. Clinton and her supporters have criticized the senator for failing to reveal how he would finance it, and they have suggested his plan would raise taxes on middle class families. 

"I think it's very confusing, because he hasn't put forward a plan," Clinton said on "Face the Nation." "I do think there are very legitimate questions that can be raised, and because we don't have an up-to-date plan from Sen. Sanders, all of us [are] trying to figure out what it would mean for everybody to be put into that new system."

Sanders defended his plan, saying on "State of the Union" that it would "save middle-class families thousands of dollars a year on their health care costs." He criticized his opponent's daughter, Chelsea Clinton, for her comments last week that he would seek to "dismantle" the Affordable Care Act and other programs.

"I mean, Chelsea Clinton is a very, very smart and capable young woman. I'm sure she loves her mother and she's trying to do everything she can to make sure her mom wins. That's pretty natural. I have got four kids, seven grandchildren. They're rooting for me," Sanders said. "But I was a little disappointed that what Chelsea said was simply not accurate."