Prominent House Democrats who have picked sides in the 2020 presidential primary plan to soon announce they will back the eventual Democratic nominee after what’s becoming an increasingly fractious race to challenge President Trump.

Rep. Brendan Boyle (Pa.), a backer of former vice president Joe Biden, is leading the effort to unify House Democrats and has so far been in touch with two of his colleagues from California — Reps. Ro Khanna and Katie Porter. Khanna has again thrown his support behind Sen. Bernie Sanders (Vt.), who has few supporters in the House, and Porter is backing Sen. Elizabeth Warren (Mass.)

When he gets back to Washington, Boyle, who campaigned for Biden in New Hampshire on Sunday, plans to ask a supporter of former South Bend, Ind., mayor Pete Buttigieg to join the group. He hopes to announce the effort soon, though specific timing is still undecided.

“Essentially, I had the idea that friends of mine I serve with in the House and who are prominent supporters of other candidates would join me in a united effort to make sure we all vigorously back whichever candidate wins our primaries,” Boyle said Sunday in an interview. “The goal of this is to absolutely avoid a repeat of 2016, when lingering bad feelings from the primaries hurt us in the general election and we ended up losing a close race. That is a luxury we absolutely cannot afford.”

Boyle was referring to the difficulty Democrats had in uniting after Hillary Clinton won a bruising 2016 intraparty fight over Sanders, some of whose supporters claimed the race was rigged in her favor and were reluctant to coalesce behind her. With Sanders rising in a key Iowa poll, some observers fear a similar dynamic will replay itself this cycle.

Khanna, reached while campaigning for the independent senator in Iowa, echoed Boyle’s sentiment that Democratic members should rally behind the eventual nominee and forge consensus among different parts of the party.

“We need to send a clear message that this party will be unified,” Khanna said in an interview, adding that Boyle has been a “very constructive force in the House” in bringing together members. “The only thing that would make our nominee unelectable is if our party doesn’t unify, so let’s not make that a self-fulfilling prophecy.”

The Democratic race is becoming more contentious following the release Friday of a new Des Moines Register and CNN poll taken ahead of the Feb. 3 Iowa caucuses. The survey showed Sanders with a narrow lead at 20 percent compared with a second-place finish by Warren at 17 percent. Buttigieg placed third in the survey at 16 percent, followed by Biden at 15 percent.

As Sanders has risen in the polls, some traditional Democrats have voiced growing concerns about his candidacy. They worry he will polarize the electorate and give Trump and other Republicans an opening in battlegrounds across the country, including many of the suburban areas where Democrats won back control of the House in 2018.

Jim Messina, President Barack Obama’s 2012 campaign manager, told Politico that Trump would relish a race against Sanders because he could easily be labeled a “socialist.”

Earlier Sunday, Warren condemned the Sanders campaign for developing a negative script criticizing Warren for appealing to “highly educated, more affluent people.” She criticized the “factionalism” that affected the 2016 election, suggesting that Sanders’s campaign ultimately hurt Clinton in the general election against Trump.

Sanders and his allies have dismissed these arguments, insisting the only way to defeat Trump is to generate excitement in the party and attract new and nontraditional voters. He also has promised to rally behind whoever wins the Democratic nomination.

And his own campaign is launching attacks at other Democrats, including Warren, with whom he has shared a nonaggression pact for most of the primary. This weekend, his campaign intensified its attacks on Biden for his past positions on racially charged issues and for supporting the Iraq War.

Trump also weighed in with a tweet Sunday afternoon, and a campaign aide told The Washington Post to expect more attacks on Sanders in the coming days.

The senator from Vermont is running to enact sweeping changes, including the creation of a health-care system in which the government would be the sole insurer. Known as Medicare-for-all, the plan has stoked impassioned debate in the party, drawing criticism from some Democrats who worry it will alienate the swing voters who helped deliver the House majority in 2018 to candidates who ran on more incremental changes.

House Democratic leaders credit their success in the last cycle to a blueprint emphasizing noncontroversial “kitchen table” issues designed to draw support from Republicans turned off by Trump’s controversies. But Sanders and his allies are advancing a strikingly different strategy. From enacting a federal jobs guarantee to eliminating all student-loan debt, they are discussing ideas rarely broached by successful House candidates in the midterms. Their plans are estimated to costs tens of trillions of dollars and require tax increases, mostly on wealthy Americans.

Sanders and his supporters make no apologies for their approach. At a campaign stop last year, Rep. Alexandria Ocasio-Cortez (N.Y.), Sanders’s highest-profile surrogate, explained her view of the electorate.

“There’s two kinds of swing voters,” said Ocasio-Cortez as she introduced Sanders at a rally in Nevada in late December. “There’s the classic one that people like to think of — blue to red and red to blue. ... But the swing voter that we are most concerned with are the nonvoters to voters. That swing voter is going to win us this election and the general election.”

Some of the tensions between Sanders and Democratic leaders eased after his bruising campaign against Clinton in 2016, but the friction is still apparent at his campaign events. Sanders has continued to rail against the party establishment and many of his backers say they distrust party leaders.

On Sunday, Sanders took aim at Messina. “Last I heard, he was over in England working for the Conservative Party,” Sanders said.