Sen. Bernie Sanders, I-Vt., told ABC News on Sunday that he is more progressive than one of his chief rivals for the status of frontrunner for the Democratic presidential nomination, former Vice President Joe Biden.

"I think if you look at Joe’s record and you look at my record, I don’t think there’s much question about who’s more progressive," Sanders told ABC News Chief White House Correspondent Jonathan Karl during his appearance on "This Week." Although Sanders said that he considers Biden to be a "good friend" and did not want to "attack" him, he insisted that he felt Biden's recent comment that the former vice president had "the most progressive record" of all the Democratic presidential candidates was in error.

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"Joe voted for the war in Iraq, I led the effort against it. Joe voted for NAFTA and permanent trade relations, trade agreements with China. I led the effort against that. Joe voted for the deregulation of Wall Street, I voted against that," Sanders said when elucidating the policy differences between himself and Biden.

The Vermont senator also focused on one of his signature issues, health care reform, and explained the difference between his support for Medicare for All and Biden's approach to health care policy, which emphasizes a public option in which private individuals can buy into Medicare and modifying the Affordable Care Act, President Barack Obama's landmark health care law.

"[T]he system today is truly dysfunctional. All that I want to do is expand Medicare over a four year period. To cover every man, woman and child in this country…. if you want a better program, a more comprehensive program, with no deductibles, with no copayments, with no premiums, which will cost your family less, support Medicare for all," Sanders told Karl.

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Sanders also had positive words for his chief rival among the party's progressive wing, Sen. Elizabeth Warren of Massachusetts.

"I think Elizabeth Warren is a very good senator. She is a friend of mine. She's a serious candidate. She's a good candidate. We have differences; we agree on a lot of things. We’ll let the voters sort it out," Sanders told Karl.

In a campaign speech last week in Pittsburgh, Biden explained that his position on health care is that "whether you're covered through your employer or on your own or not, you all should have a choice to be able to buy into a public option plan for Medicare… Your choice. If the insurance company isn't doing the right thing by you, you should have another choice."

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An adviser to Biden further clarified the former vice president's position by telling the Washington Post that "we are all trying to get to a place where we achieve universal health care. I think he sees it like that. But if they want to go after him and Obama about their approach to health care, bring it on."

Polls have consistently found Biden among the frontrunners for the 2020 presidential nomination, if not at the very top of the list. Other strong contenders have included Sanders, Warren, Sen. Kamala Harris of California, Rep. Beto O'Rourke of Texas and Mayor Pete Buttigieg of South Bend, Indiana.