Elizabeth Warren is best known as a liberal firebrand, but the 2020 Democrat was a registered Republican well into her 40s.

The Massachusetts senator's affiliation with the GOP until 1996 when she was 47, documented by Pennsylvania and Massachusetts voting records, was dredged up this week by actress and Bernie Sanders fan Susan Sarandon. The film and small-screen star alluded to the Massachusetts senator's prior party allegiance while introducing Sanders in Iowa, despite the Vermont senator's campaign urging surrogates not to criticize fellow presidential candidates.

“He is not someone who used to be a Republican,” Sarandon said of the socialist, who himself has toggled between being a Democrat and independent before and after elections.

Sarandon's comments come as Warren, 70, continues to ingratiate herself to Sanders' base as a consummate darling of the Left amid her fight for the right to challenge President Trump next year.

Morning Consult's latest weekly report analyzing the 2020 Democratic primary field showed Warren has doubled her approval among potential voters who identify as being "very liberal" since February, with her and Sanders notching up 25% apiece. The firm surveyed 17,115 interviewees online between Aug. 12 and Aug. 18, with a margin of error of plus or minus 1%.

Oklahoma-born Warren has weaved recollections of her family's financial struggles into her stump speech and refers to her older brothers' continued ties to the Republican Party when grilled on the trail about how she would reach out to all voters given her populist rhetoric (she told the Intercept last year her parents were New Deal Democrats). Yet she rarely mentions her own GOP connection before she moved to Massachusetts to teach at Harvard Law School. She was, however, pressed about her Republican association ahead of her 2012 win against incumbent GOP Sen. Scott Brown for the late Sen. Ted Kennedy's seat in the upper chamber.

“I was a Republican because I thought that those were the people who best supported markets. I think that is not true anymore,” Warren told the Daily Beast in 2011. “I was a Republican at a time when I felt like there was a problem that the markets were under a lot more strain. It worried me whether or not the government played too activist a role.”

"I felt like the parties were moving and the conversation was moving,'' she said to the Boston Globe in 2012. "I felt like I had stayed in the same place and the world had shifted around me.''

Regardless of her Republican leanings, Warren has insisted when she did vote, the only GOP nominee for whom she cast a ballot in the six White House races before 1996 was Gerald Ford in 1976. In fact, she was registered as an independent for a period while she lived in Texas and backed Jimmy Carter in 1980.

“I voted — sometimes voted for Democrats, sometimes voted for Republicans — but never thought of myself, never had to frame myself, in political terms," she told Politico in April.

The twice-married, mother of two, and grandmother of three bankruptcy law expert has attributed her political awakening to decades spent researching debt and her experience from 1995 advising the National Bankruptcy Review Commission. She had previously likened burdensome government regulation to a "tax" in a 1993 interview with the Philadelphia Inquirer, according to an article unearthed last weekend by CNN. But any illusion of nonpartisanship was shattered when the George W. Bush administration ignored the commission's consumer-centric recommendations in favor of the pro-business Bankruptcy Abuse Prevention and Consumer Protection Act.

"I was an independent. I was with the GOP for a while because I really thought that it was a party that was principled in its conservative approach to economics and to markets. And I feel like the GOP party just left that. They moved to a party that said, 'No, it’s not about a level playing field. It’s now about a field that’s gotten tilted.' And they really stood up for the big financial institutions when the big financial institutions are just hammering middle class American families. I just feel like that’s a party that moved way, way away," she told ABC News in 2014 as she promoted her memoir, A Fighting Chance.

The Wall Street critic would go on to evaluate the federal bank bailout after she was appointed chairwoman of the Congressional Oversight Panel by former Senate Majority Leader Harry Reid in 2008. She would later become pivotal to the establishment of the Consumer Financial Protection Bureau in 2010.

The effectiveness of attacks aimed at Warren's past remains to be seen as the primary battle draws closer to the Iowa caucuses in February. Former Vice President Joe Biden has more than a 13 percentage point advantage on the senator, who currently earns an average of 15.8% in RealClearPolitics' polling data. That level of support puts her a touch ahead of Sanders, who amassed 15.4% as of Tuesday afternoon.