Here's what Tom Steyer said about the 'awkward moment' he witnessed between Sanders and Warren

Seconds after the debate ended, Warren was seen shaking hands with Steyer and former Vice President Joe Biden, but when Sanders extended his hand, Warren didn't take it. Instead, she appeared to engage him in an animated conversation.

The tense interaction came after Warren and Sanders offered dueling accounts of the contents of a conversation at a private 2018 dinner. Warren -- who has confirmed what four sources told CNN about the meeting -- stood by her account that Sanders told her a woman could not win the presidency while Sanders held that he never made the remark.

"I was just going up to say 'good night Sen. Sanders' and I felt like, OK, there's something going on here. Good night, I'm out of here," Steyer told CNN's Anderson Cooper following the debate.

"I really wasn't listening. They were talking about getting together or something," Steyer said. "I really didn't listen. I really -- it was one of those awkward moments where I felt like, you know, I need to move on as fast as possible."

He added, "My goal was simply to say good night to two people who I respect. The last thing I wanted to do was get between the two of them and listen in. That was not my goal and I didn't do it."

When asked by CNN what Warren said to Sanders as the debate ended, Sanders campaign co-chair Nina Turner said, "I'm not sure what she said, but you can read the body language. Obviously their conversation was not pleasant."

While Warren and Sanders had previously taken careful efforts to manage their friendship and political rivalry, percolating tension between the two was laid bare at the debate when Warren used a question about the 2018 meeting to underscore the electoral prowess of the female candidates on the debate stage.

"But look, this question about whether or not a woman can be president has been raised and it's time for us to attack it head-on," Warren said. "I think the best way to talk about who can win is by looking at people's winning record. So, can a woman beat (President) Donald Trump? Look at the men on this stage: Collectively, they have lost 10 elections. The only people on this stage who have won every single election that they've been in are the women."

The bust-up began on Sunday after Politico reported that some volunteers for the Sanders campaign had been given talking points suggesting that Warren's support did not extend beyond "highly educated, more affluent people." Asked about it later in the day, Warren accused Sanders of "sending his volunteers out to trash me."