Bernie Sanders and Joe Biden go back a long ways. But the two Democratic front-runners are going to have to put aside their friendly relationship as they each vie to be the Democratic Party’s nominee in the 2020 presidential election.

And when it comes to who is the more progressive candidate, Sanders says it’s not even a close contest.

“I think that if you look at Joe's record and you look at mine I don't think there's a question about who's more progressive,” the Vermont senator said Sunday during an interview on ABC’s “This Week.”

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Sanders, who added that he was not on the show to attack the former vice president, rattled off a list of issues where the two took different approaches.

“Joe voted for the war in Iraq, I led the effort against it,” Sanders said. “Joe voted for NAFTA and trade agreements with China. I led the effort against that.”

Sanders added: “I disagree with many of the votes that he cast.”

Sanders, however, echoed Biden’s words from a fundraiser in South Carolina that he wants the 2020 campaign to focus on issues affecting American voters and not on personal slights and attacks.

“I hope on the democratic side that the campaign is about a discussion of issues, not personal attacks,” Sanders said. “I think that I feel safe to say that no matter who the candidate is we're all going to come together to defeat the most dangerous president in modern American history and that is Donald Trump.”

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Biden, during a private fundraiser in South Carolina on Saturday, criticized Trump for engaging in personal battles with political rivals instead of focusing on issues.

“On every single issue and on every demeaning thing he says about other people, I have no problem responding directly,” Biden said. “What I’m not going to do is get into what he wants me to do. He wants this to be a mud wrestling match.”

Biden, however, did give Trump a nickname when pressed by a guest at the fundraiser.

“There’s so many nicknames I’m inclined to give this guy,” Biden said. “You can just start with clown.”