WASHINGTON — Vice President Joe Biden called Sen. Cory Booker on Wednesday night in an attempt to smooth things over after the two presidential candidates got into a public dust up after the former vice president had talked about his work with segregationist senators, multiple sources told NBC News.

Biden phoned Booker following the New Jersey senator's appearance on CNN on Wednesday night. That appearance took place after Biden had reacted to Booker criticizing him earlier in the day and calling on Biden to apologize for remarks he made about his work with Sens. James Eastland of Mississippi and Herman Talmadge of Georgia, both Democrats who were staunchly opposed to desegregation.

"Apologize for what? Cory should apologize," Biden said. "He knows better. There's not a racist bone in my body."

On CNN, Booker shot back, "For someone to show the lack of understanding or sensitivity to even know when they've made a mistake and to fall into that kind of defensive posture — that I should apologize to him — is really problematic. I was raised to speak truth to power. And I will never apologize for doing that. And Vice President Biden shouldn't need this lesson."

During their phone call, Biden did not ask for an apology from Booker and neither candidate offer one to each other, two sources familiar with the call told NBC News.

The back-and-forth began after numerous Democratic presidential candidates began lambasting the vice president for recounting his attempt to work with Eastland and Talmadge to get "things done" during a time of what Biden called "civility" in the Senate during the 1970s and 80s.

"Cory shared directly what he said publicly — including helping Vice President Biden understand why the word 'boy' is painful to so many. Cory believes that Vice President Biden should take responsibility for what he said and apologize to those who were hurt," Booker campaign spokeswoman Sabrina Singh told NBC News.

That was a reference to Biden's comment to supporters, "I was in a caucus with James O. Eastland. He never called me 'boy.' He always called me 'son.'"

Booker discussed the phone call in an appearance on Thursday night on MSNBC's "The Last Word" with Lawrence O'Donnell.

He again said Biden should apologize for his comments: "This is something he should speak to the public about...I believe he should apologize to the American people."

Booker said their conversation lasted 15-20 minutes and was "constructive."

"I feel very strongly what I know is that Joe Biden should not need to be explained to about why that word ('boy') is so hurtful, why what he said would be something that people would find offensive and harmful," he said.

"At the end of the day, this is not about me, this is not about him, it's about where our country is and we have real race issues in our country, and we need leaders, plural, presidential candidates or not, that can bring folks together, can deepen understanding and empathy, and can get us to a point where we can begin to work on a lot of the issues that have deep, scarred legacies in our country."

On Thursday night, Biden also met with members of the Congressional Black Caucus. Biden did not answer questions from the press as he was leaving the meeting.