Democratic presidential hopefuls Massachusetts Senator Elizabeth Warren (L), former Vice President Joe Biden (C) and Vermont Senator Bernie Sanders participate of the seventh Democratic primary debate of the 2020 presidential campaign season co-hosted by CNN and the Des Moines Register at the Drake University campus in Des Moines, Iowa on January 14, 2020.Robyn Beck | AFP | Getty ImagesThings got testy between Sen. Bernie Sanders and Sen. Elizabeth Warren on Tuesday night. First, Sanders denied during the Democratic debate that he told that a woman could not be president, pointing to his record and a video on YouTube as evidence.Warren, in turn, pointed out that the women on stage had done better in elections than their male rivals.The exchange came after a day of controversy over Warren’s claim that Sanders had told her in a private meeting before she announced her White House bid that a woman couldn’t win the presidency. Sanders denied that he said it.That tension appear to spill past the end of the debate.As the candidates shuffled off the stage to mingle with supporters, Warren approached Sanders but declined to shake his outstretched hand. She spoke a few words, causing Sanders to furrow his brow and appear to say “what?” before raising his hands and responding.Sanders then raised both his hands higher and turned away from Warren to shake hands with Tom Steyer, another candidate who was standing close by.The exchange between Warren and Sanders was inaudible and lasted just a few seconds, but it was captured on video.According to NBC News, Steyer said he didn’t know what the two said and that he “was trying to get out of the way as fast as possible.”Spokesmen for Warren, Sanders and Steyer’s campaigns did not immediately respond to CNBC’s inquiries about the exchange.”Anybody who knows me knows that it’s incomprehensible that I would think that a woman could not be the president of the United States,” Sanders said.The Vermont senator, who identifies as a democratic socialist, added that in 2015 he chose to hold off on announcing his candidacy for president, until Warren told him she would not run in the 2016 election.”Warren decided not to run and I did. I ran afterwards,” he said.Sanders said that if any of the men or women on Tuesday’s debate stage – Warren and Sen. Amy Klobuchar were the only women there, as Rep. Tulsi Gabbard didn’t qualify – win the nomination, “I will do everything in my power to make sure they are elected in order to defeat the most dangerous president in the history of our country.”Warren, in her response to Sanders, pivoted away from her private conversation with Sanders, instead choosing to focus on the records of the women on stage.”Look at the men on this stage,” Warren said. “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. Amy and me.”The Massachusetts senator also said that she’s “the only person on this stage who has beaten an incumbent Republican anytime in the past 30 years.””We need a candidate who will excite all parts of the Democratic party, bring everyone in, and give everyone a democrat to believe in,” she said.Sanders disputed her claim by saying he had indeed defeated an incumbent Republican in a congressional race – 30 years ago.Subscribe to CNBC on YouTube.