A progressive group is urging supporters of Sens. 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.) and 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.) to back the other candidate in the Iowa caucuses on Monday should their preferred candidate not reach the required threshold to be counted.

Charles Chamberlain, chairman of Democracy for America (DFA), which has voiced support for both Sanders and Warren in the 2020 race, emphasized that Democrats should be united behind the progressive candidates heading into the caucuses.

“What we’re saying is if you’re a supporter of a candidate who gets less than 15 percent, then it’s absolutely critical that you don’t go home — make sure you move to one of the top two progressives, so that we make sure that a progressive wins the caucus," he said.

During the first round of the caucus, caucus goers walk around and stand in different areas indicating their support for a candidate. Candidates who fail to secure 15 percent of the total voters are removed and their supporters can then back another contender.

“Making sure that we’re supportive of all of the progressives that are in this race and that we’re not attacking our own is really important because President Sanders or President Warren’s going to need Sen. Sanders or Sen. Warren to make sure to actually pass their agenda and that’s the best situation we could be in,” Chamberlain said.

DFA was among a number of progressive groups who signed a three-part unity pledge vowing to focus their fight on the “corporate wing” of the Democratic Party, ensure that a progressive candidate wins the party's presidential nomination and that they'd join forces to make sure the candidate they back defeats President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE.

The move came after Sanders and Warren became embroiled in a bitter dispute earlier this month.

Though the two progressives had agreed not to attack one another, that comity broke down after reports that Sanders’s campaign was instructing volunteers to question whether Warren was electable.

Warren later alleged that Sanders told her in a private meeting in 2018 that a woman could not win the White House. Sanders, meanwhile, has denied ever making such a claim.

The spat culminated in an exchange following the Iowa debate. Warren confronted Sanders on the debate stage, and accused him of calling her a “liar on national TV.”

It is unclear whether the two candidates have spoken since, though Sanders’s campaign co-chair Rep. Ro Khanna Rohit (Ro) KhannaThe Hill Interview: Jerry Brown on climate disasters, COVID-19 and Biden's 'Rooseveltian moment' Congress needs to prioritize government digital service delivery DeJoy defends Postal Service changes at combative House hearing MORE (D-Calif.) came to Warren’s defense amid the public fallout and joined calls for unity.

“There are ups and downs in campaigns, but I have tremendous admiration and respect for Sen. Warren,” Rep. Ro Khanna (D-Calif.) told Hill.TV, noting Warren’s record on anti-corruption and founding of the Consumer Financial Protection Bureau.

Both progressive heavyweights have polled near the top of the Democratic field for most of the primary race, though Warren appears to have lost some momentum recently in state and national polls while Sanders has seen a surge going into the Iowa caucuses.

A New York Times/Siena College poll released on Sunday showed Sanders with 25 percent support followed by former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBipartisan praise pours in after Ginsburg's death Bogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq MORE at 18 percent, former Vice President Joe Biden Joe BidenBiden leads Trump by 36 points nationally among Latinos: poll GOP set to release controversial Biden report Can Donald Trump maintain new momentum until this November? MORE at 17 percent and Warren at 15 percent.

However, other Iowa polls show Biden holding a narrow lead. According to a poll by Park Street Strategies, the former vice president garners 20 percent support and is trailed by Sanders with 18 percent. Warren and Buttigieg were tied at 17 percent each.

—Tess Bonn