A top adviser to Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.) on Tuesday took a swipe at Sen. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.) over the senator's affiliation with the Republican Party decades ago.

The remark from Nina Turner, a former Ohio state senator and the co-chairwoman for Sanders’s presidential campaign, comes amid rising tensions between the two leading progressives in the Democratic primary race.

Turner’s comments came after Warren asserted during Tuesday night’s Democratic presidential debate that she was the only candidate on stage to have defeated a Republican incumbent at any point in the past 30 years.

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That sparked a brief exchange with Sanders, who noted that he had defeated an incumbent Republican in 1990, the year he first won election to the House.

“Thirty years ago?” Warren asked. “I said I was the only one who's beaten an incumbent Republican in 30 years.”

Asked after the debate about whether Warren’s remark was unfair to Sanders, Turner took a jab at the Massachusetts senator.

“You should ask [Warren] that, but I know 30 years ago she was a Republican,” Turner told reporters, according to HuffPost.

Turner's comment came as tensions have mounted between Sanders and Warren after news reports emerged that Sanders told Warren during a private dinner in December 2018 that he did not believe a woman could win the presidency.

Warren appeared to confirm those reports on Monday, recalling how Sanders had “disagreed” with her when she told him she believed a woman could win the White House.

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Sanders denied that account of the dinner at Tuesday's debate, saying that “it is incomprehensible that I do not think a woman could be president of the United States.”

Indeed, Warren was registered to vote as a Republican until 1996. She has spoken openly about that switch, telling The New York Times last year that prior to becoming a Democrat, she was not particularly engaged with politics.

It was only after she went to Capitol Hill, she told the newspaper, that she “picked sides” and “got in the fight.”

“I quickly discovered that every single Republican was on the side of the banks and half the Democrats were,” Warren told the Times. “But whenever there was someone who would stand up for those working families, it was a Democrat.”