This is the first sign that Joe Biden may drop the Uncle Joe routine for the 2020 Democratic primary and go back to being the ruthless political knife fighter that he was in the U.S. Senate.

In a CNN interview that airs Friday, Biden casually mentioned that his campaign has been collecting dirt on his 2020 primary opponents. He said he wants to focus on the issues and that he does not want to go low, but he was also sure to let slip that he knows where the bodies are buried.

The moment occurred as CNN’s Chris Cuomo brought up the beating Biden took at the second Democratic debate last week, when Sen. Kamala Harris savaged the former vice president for his past opposition to the busing of students for the purpose of racial desegregation.

“[D]id you see the questions about your past positions from the perspective of race being as relevant as they are?” asked Cuomo.

Biden responded, “No, I don’t think they’re relevant, they’ve been taken out of context. What I didn’t see is people who know me. I mean, they know me well, it’s not it’s somebody who just came out of the blue and didn’t know anything. It’s so easy to go back, and go back 30, 40, 50 years and take it completely out of context.”

The 2020 Democratic front-runner added in a not-so-subtle note [emphasis added], “And I mean, I get all this information about other people’s pasts, and what they’ve done and not done. And you know, I’m just not going to go there. If we keep doing that — I mean, we should be debating what we do from here.”

Uh-huh.

Most people are smart enough to know a threat when they hear one.

Biden tacitly acknowledged that his campaign has been ransacking his 2020 opponents’ closets and that his aides have amassed a tidy pile of skeletons. More importantly, Biden made sure to mention that he is aware of said skeletons. His supposedly off-hand remark can be read as: If you want to keep coming after me, Harris, Cory Booker, Pete Buttigieg, et cetera, I know your dirty secrets.

It makes sense that Biden would go down this route. He failed badly in the second Democratic primary debate. He looked weak, unprepared, and out of practice. He was not ready for Harris’ attack, and he said as much in his interview with Cuomo. Moreover, surveys conducted since the debate have shown that Biden's lead in the primary may be fragile. He is angry and righteously indignant. And Biden also knows how to play rough, his 10-plus-year dedication to playing the role of the affable uncle notwithstanding.

He may not now be the killer he once was – even the best pitchers lose their fastball with age — but he may still have a little juice leftover from his Senate days of destroying adversaries with vicious smears and innuendo. It could all be just an idle threat, but don’t forget that Biden was at one time quite skilled in the art of throwing political opponents into the wood chipper.