Adam Green, co-founder of the Progressive Change Campaign Committee (PCCC), offered an argument in a Wednesday interview on SiriusXM Radio why Sen. Elizabeth Warren Elizabeth WarrenGOP set to release controversial Biden report Biden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (D-Mass.), who his group is supporting, would be a more effective president than Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE (I-Vt.).

Warren, who has trailed Sanders in the Democratic contest so far, argued at Tuesday night's debate in South Carolina that she should be the progressive nominee for Democrats — and not Sanders — because she had a better track record of getting things done.

Green sought to boost that argument in the interview with Zerlina Maxwell on "Signal Boost."

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He offered an anecdote about interactions Green and his group had with Sanders in 2015, when Sanders was backing an infrastructure funding proposal but ended up introducing a bill with little political support.

"On Jan. 21, 2015, myself and my co-founder, Stephanie Taylor, and some folks from our legislative team met with Bernie Sanders ... and we showed him some polling that we had done, the Big Ideas Poll, showing that so many big, progressive ideas were popular," Green said.

Green noted that one of the questions in the poll related to infrastructure reform, which led Sanders to inform him that he was introducing a "trillion dollar infrastructure bill" (Rebuild America Act of 2015) the following week.

"After the meeting we begged his office, 'Can you please delay this for a couple weeks? Let us help you lobby for co-sponsors. Let us help you get other grassroots groups on board.' " Green continued.

"But he was insistent. He must introduce his bill on Tuesday. And sure enough, at the press conference he had one co-sponsor, he had one main endorsing group, the engineers," Green said. "That was January 2015 and the entire Congress of 2015 and 2016, there were zero other co-sponsors that got on board and almost no movement around the bill."

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Green then shifted to the accomplishments of Warren, saying "when I think about that versus what Elizabeth Warren did with the Consumer Financial Protection Bureau, where she had an idea, she did the hard work of organizing it on the inside of Congress."

He added: "Passing the crown jewel of Wall Street reform into law to create this consumer agency that would go to bat against big banks and predatory lenders and credit card companies ... go to bat for the little guy, win back $12 billion for 29 million Americans that were cheated. ... The difference in effectiveness between those two things is just night and day."

Despite being championed by the PCCC as the go-to progressive candidate in the Democratic presidential primary race, Warren has middled in the first three primaries, finishing third in Iowa and fourth in both New Hampshire and Nevada.

Sanders, on the other hand, has surged to front-runner status after virtually tying for first in Iowa and winning New Hampshire and Nevada outright.

The last primary before Super Tuesday on March 3 is South Carolina on Saturday.

Warren has sharpened her attacks on Sanders in recent weeks, casting the Vermont senator as a rigid ideologue who won't be able to enact his progressive agenda because he doesn't have strong relationships with other lawmakers.

There have been growing tensions between supporters of Sanders and Warren, the two candidates most closely associated with the progressive left. Warren earlier this year accused Sanders of telling her that a woman could never win the White House.

Sanders has not gone on the attack much against Warren, but he'll hold two rallies in her home state this weekend. Massachusetts is a key state to vote on Super Tuesday, and candidates are expected to win in their home states.

The Sanders campaign declined to comment on Green's interview.

Jonathan Easley contributed.