Bernie Sanders builds momentum with progressive groups ahead of Iowa caucus originally appeared on abcnews.go.com

With less than three weeks until voting starts in Iowa and beyond, the campaigns of both Sen. Bernie Sanders and Sen. Elizabeth Warren are jockeying for support from the progressive wing of the Democratic Party.

The two candidates have been friends for nearly 20 years and have, until now, maintained a pact of non-aggression during the 2020 race. Earlier this week, Sanders vehemently denied reports, including a statement from Warren herself, that he said a woman couldn't win against Donald Trump.

On Monday, Democracy for America, a progressive organization, called on the two candidates to cool down their rhetoric.

“Bernie Sanders and Elizabeth Warren, you both are progressive champions and our movement needs to see you working together to defeat your corporate Democratic opponents – not attack each other,” the group tweeted. “Progressives will win in 2020, but only if we don’t let the corporate wing or Trump divide us.”

However, the escalating of tensions between the two progressive, veteran lawmakers comes as Sanders builds momentum with a slew of progressive endorsements ahead of the Iowa caucus.

The Sanders campaign snagged endorsements within the past week from immigrant rights group Make the Road Action, youth-led environmental group the Sunrise Movement and advocacy group for people of color Dream Defenders.

PHOTO: Democratic presidential candidate Senator Bernie Sanders hosts a climate rally with Rep. Rashida Tlaib and Rep. Ro Khanna in Iowa City, Iowa, Jan. 12, 2020. (Scott Morgan/Reuters) More

“We can and we must fight for a country where members of our communities are free to stay, free to move, and free to thrive," said Javier Valdés, Co-Executive Director of Make the Road Action. "And we are proud to fight alongside Bernie Sanders to realize that vision.”

Sunrise Movement co-founder and executive director Varshini Prakash campaigned for Sanders in Iowa.

“We endorse Bernie Sanders because he stands for a Green New Deal,” said Prakash at a rally in Iowa City.

Prakash cited Sanders' pledge to address climate change, racial inequity, immigration and health care during her speech.

“Bernie’s track record is consistent,” read a statement from the Dream Defenders announcing their endorsement of Sanders’ presidential bid. “Throughout his career, he has pushed visionary ideas long before they were politically popular.”

(MORE: 3 weeks before Iowa caucus, candidates' closing arguments come into focus)

PHOTO: Democratic presidential candidate Sen. Bernie Sanders is welcomed to the stage by Sunrise Movement co-founder Varshini Prakash, right, at the Graduate Hotel, Jan. 12, 2020, in Iowa City, Iowa. (Andrew Harnik/AP) More

Those endorsements are only the most recent.

The Sanders campaign can boast endorsements from the Center for Popular Democracy Action, People’s Action, and several labor unions. Rep. Alexandria Ocasio-Cortez, Rep. Rashida Tlaib and Rep. Ilhan Omar, members of the so-called “squad” of progressive freshman congresswomen of color, have stumped for Sanders on their home turfs and in early voting states.

“We earned those endorsements because of the long history of the senator fighting on behalf of and alongside these communities for issues they care about,” said Sanders' National Political Director Analilia Mejia.

“We communicated extensively in regards to policy platforms and in regards to issue campaigns that they were working on, and we made them part of the campaign, even before they endorsed, by way of soliciting their input,” Mejia said.

Securing these endorsements is important to rallying potentially millions of people behind a candidate, according to ABC News contributor and Democracy for America CEO Yvette Simpson.

“I think the progressive grassroots endorsements mean so much more than just $1, or a name on a website, or whatever,” Simpson told ABC News. “Because it comes with all of that power, real people ready to activate and mobilize behind these candidates.”

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